All-around protection for your little one
Perfectly tailored to the needs of children from 76 cm to 105 cm tall, TRIFIX² i-SIZE is the ideal follow on seat to any infant carrier. Easily and safely installed thanks to its integrated ISOFIX connectors and Top Tether, its optimised seating area ensures that there’s enough space for a growing child from 15 months up to about 4 years. And with a unique range of advanced safety features you can rest assured that your child will be well protected.


Baby Toddler Child

i-Size (ECE R129)

76 cm - 105 cm

8 kg - 22 kg

15 months - 4 years


  • Made in Germany

TRIFIX2 i SIZE MoonlightBlue 02 2017 72dpi 2000x2000





i Size Logo


Fitting a car seat 100% safely can be tricky because every car is different. That’s why Britax co-developed ISOFIX, a standard system of connection points featured in almost all cars. The ISOFIX system establishes a secure and firm connection between the child’s car seat and the car. So every time you, or a grandparent or friend, have to fit the car seat into your car, or into another car, fewer mistakes can be made.

TRIFIX² i-SIZE specific requirements - a safe installation is completed with the use of Top Tether to allow optimum stability.

Our i-Size car seats will fit all i-Size approved seating positions, so please check your vehicle owner's manual for i-Size approved seating positions.

top tether 20x20 new aw

ISOFIX and Top Tether

Fitting a car seat 100% safely can be tricky because every car is different. That’s why Britax co-developed ISOFIX, a standard system of connection points featured in almost all cars. The ISOFIX system establishes a secure and firm connection between the child’s car seat and the car. So every time you, or a grandparent or friend, have to fit the car seat into your car, or into another car, fewer mistakes can be made.

TRIFIX² i-SIZE specific requirements - a safe installation is completed with the use of Top Tether to allow optimum stability.

Check the vehicle owner's manual to locate ISOFIX and Top Tether anchorage points in your car and ask your local retailer for a test installation in your car (please ask for a member of staff trained by Britax) before you buy the car seat.


Forward facing installation

76 cm - 105 cm


Superior Side Impact Protection
01 FEATURE SICT inside TRIFIX i SIZE 1180x830px 72dpi

The integrated SICT inside offers your child superior protection in the event of a side collision. SICT inside keeps your child away from the impact while absorbing energy at the same time. And you don’t have to adapt or adjust anything – SICT inside is always ready when you need it.

The Britax Römer Pivot Link System
Feature07 Pivot Link ADVANSAFIX III SICT 1180x830px 72dpi

In case of an impact, our patented Pivot Link System directs the force first downward, into the vehicle seat, and then forward, more gently – greatly reducing the risk of head and neck injury.

Top Tether with rip-stitch technology
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Our v-shaped Top Tether prevents the seat from rotating and reduces the forward movement of the child in the event of a collision. Due to its twin anchorage points, it offers even greater stability and security for your child than a seat with conventional tethers. Plus, its unique pattern of stitches is designed to progressively rip in a controlled fashion, absorbing the force of the frontal impact.

V-shaped headrest
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Specially designed to control the movement of your child’s head, our V-shaped headrest ensures optimal protection in the event of a side collision while providing ultimate comfort at the same time. Plus, the headrest and harness can easily be adjusted from the front of the seat to suit your child’s height.

Deep, protective side wings
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Our soft, padded side wings act as a protective cocoon that helps to absorb the force from a side impact, reducing the risk of injuries to your child.

5-point harness
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We believe a 5-point harness is the safest way to secure your child in a car seat because it keeps your child safe and tight in the seat’s protective shell. In case of a collision, the harness distributes the forces of the impact across 5 points, two at the shoulders, two at the hips and one where the harness buckles between the legs. This helps to protect your child from all directions of impact.

Soft neoprene performance chest pads
07 FEATURE Neoprene Chest Pads TRIFIX i SIZE 1180x830px 72dpi

Our new, soft neoprene performance chest pads fit comfortably on your child’s chest. They help reduce your child’s movement in the event of a collision, and add even greater comfort to the 5-point harness. Plus, they can be easily removed for washing without disturbing the harness.

Multi-recline positions
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Keeping your child comfortable while traveling is a must. That’s why this seat was designed with four recline positions that you can adjust with ease – offering a stress-free journey with a happy child.


Montagu Montagu


H x W x D
65 x 45 x 54 cm

10.5 kg


i-Size (ECE R129)





Not every seat fits in every car. To ensure that you pick the right seat, just choose your car to see if the TRIFIX² i-SIZE fits.




This means the car seat adheres to the strict European safety standards. You can also check out the safety ratings given to most seats by European testing organisations like Stiftung Warentest, Which? and ADAC.


Our FIT FINDER® is a comprehensive car fitting tool that will help you check that our car seat is compatible with your car. This is a vital step both in ensuring that the car seat’s safety features will all be able to function in your vehicle, and also to ensure that you are fully insured should any accident occur.

Use our FIT FINDER® tool


We appreciate that car seats are complex things. But we also believe it’s important for parents to make informed choices about the type of protection they offer your child. So we’ve pulled together some of the key safety features to consider in choosing your car seat.

What kind of harnessing does it offer? 5-point harness, 3-point harness or a vehicle adult seat belt? Understand the difference between harness and shield systems – and why at Britax we only use harness protection.

Does it offer advanced side impact protection? In case of a common form of collision – from the side.

Does it offer superior head and neck protection? To protect a growing child’s vulnerable head and developing neck muscles.

Does it offer extended rearward facing travel? Proven to be the safer way to transport smaller children (and a legal requirement until 9kg).

Find out more about our safety technologies


For safety reasons, you should keep your child in each stage for as long as possible – until they reach the weight limit or the head reaches the top of the seat. This is especially important for babies as rearward facing seats offer the safest way of travelling. The general rule of thumb of moving your child to the next group is:

Move from a Group 0 + infant carrier when your child exceeds the weight limit and can sit up unaided, or if their head is higher than the top of the infant carrier.

Move from a Group 1 seat when the upper edge of the shell is roughly at eye level of the child or your child exceeds the weight limit.

Do not move too early to a Group 2-3 seat because these seats are wider to accommodate larger children. Also a younger child's shoulders are too narrow to hold to the adult seat belt securely. A small child can therefore easily slip out from under the belt, especially when they fall asleep during the journey.

A child’s head should ideally never exceed the top of the seat shell. This is especially important when using an infant carrier in order to minimise the risk of head contact with interior components of the car should an accident occur. The recline angle of our ERWF child seats (DUALFIX, MAX-FIX II, MAX-WAY, MULTI-TECH, etc.), is more upright than in an average infant carrier, which reduces the risk of the child’s head coming into contact with the car interior.

Additionally, the child’s body is more supported over a larger surface area of the seat than they would be in an infant carrier where the child is in a flatter position. In our ERWF child seat models, the child can continue to use the seat until he or she reaches the maximum stated weight or their eye-line is level with the top of the seat shell/headrest. The child would typically outgrow the seat before reaching either one of these stages since the child’s shoulders would no longer fit beneath the headrest (found in most of our ERWF products) in its highest position.


The facts:

The first thing you will need to identify is which seats will ‘fit’ your child. This depends on the age and weight of your child. Once you’ve worked this out, your next decision is around the type of seat that will best suit your needs.

Some car seats are designed around the physiology of a specific age or weight of child. These seats offer tailored protection along with the ultimate comfort and fit. Other seats are designed to cover a much wider age range. These seats offer maximum flexibility and longevity. Only you can decide what is best for your family.

Your options:


Group 0/0+ | birth to 13kg (~12/15 months) These seats, often called an ‘infant carrier’, can be used from birth and can be connected to your pushchair. They are designed to be lightweight and portable and cocoon a small baby.

Group 0+/1 | birth to 18kg (~ 4 years) These seats are designed to be used from birth but to remain within the car. They are often bigger and heavier and can’t be connected to a pushchair. However they may fit your child until they are around 4 years or 18kg. And they may give you the option of changing the seat to forward facing once your child is ready.


Group 1| 9kg to 18kg (~ 4 years) These seats are designed for children from 9kg up to 18kg and offer a range of installation and harnessing technology.

Group1/2 | 9kg to 25kg (~ 6 years) These seats are designed for children from 9kg up to 25kg and often offer a choice of rearward or forward facing travel to suit the changing needs of a growing child.

Group 1/2/3 | 9kg to 36kg (~ 12 years) These seats are designed for children from 9kg up to 36kg and represent our longest lasting seat.


Group 2/3 |15kg to 36kg (~ 4 - 12 years) These seats, often known as highback booster seats, are designed to offer ultimate safety for older children from 15kg to 36kg.


The facts:

Since we invented ISOFIX in 1997 with Volkswagen it has become the standard for car seat installation in Europe. It greatly reduces the risk of installation error and makes transferring an infant carrier when used in combination with the base in and out of the car simple. We would always recommend an ISOFIX seat, but understand that not all cars have ISOFIX connectors. So it’s important that you clarify this before you choose your seat.

Your options:


Our ground-breaking invention with Volkswagen that enables simple, direct connection to the car’s anchorage points


Designed specifically for Group 2/3 car seats – using both ISOFIX and the car’s seat belt to direct impact forces away from your child


Our latest development of the ISOFIX system uses wider connectors to limit sideways movement, along with V-Tether anchorage at the top to reinforce stability and absorb impact forces.

Vehicle adult seat belt

Using the car’s three-point seat belt to connect the seat


The facts:

Only certain types of car seat, often called an ‘infant carrier’, can connect onto your pushchair. And all seats are not compatible with every brand or model of pushchair. If you choose the right combination then an infant carrier plus travel system can offer a flexible, cocooning way of transporting your small child on the road and pavement.

Your options:

All Britax infant carriers are compatible with all of our travel systems – and with many other leading brands of travel system.


The facts:

Current European legislation (ECE R44/04) states that a child must remain rearward facing until at least 9 months or 9kg. However at Britax we recommend that your child travels rearward facing for as long as is feasible for your child, your car and your lifestyle.

Your options:

We are proud to offer not just one of Europe’s broadest ranges of rearward facing seats, but one of the most advanced – with options to keep your child rearward facing until 25kg (or around 6 years old). We also understand that this isn’t possible for all families, so we have a range of seats that give parents the choice of when to change the direction of travel for their child.

It is mandatory to use child car seats within the EU for all children up to the heights of 1.35m or 1.5m – depending on the member state.

There are currently two legal standards in Europe:

ECE R129

i-Size (this is a new standard for group 0/0+/1 seats that will exist alongside ECE R44/04 for a number of years and sets more advanced safety standards based on more recent safety data).

ECE R44/04

To meet ECE R44/04 approval car seats are tested in frontal collisions at 50km/h and rear collisions at 30 km/h using crash test dummies and advanced measuring instruments designed to assess the levels of protection each seat offers. ECE R44/04 approved seats can all be identified by their orange approval label.


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Your seat meets the European Safety Standard. Note the last two digits: these should end in 04 (latest version) or 03. R44-01 or 02 are not legal and may not be sold or used since 2008. There are 3 types of car seat approval: universal, semi-universal and vehicle specific. ‘Universal’ means your seat is approved for installation in all cars, although you should check that the seat fits really well in your car. See below article on ‘Type Labelling’. Approval for weight (group). If a letter Y is added here, it means that the child seat features a 5-point harness system with crotch strap. European approval indicator. Indicates the country in which the approval was obtained: 1= Germany 2 = France 3 = Italy 4 = The Netherlands etc. Approval number. The first two numbers (04) show to which version the child seat has been approved, in this case ECE R 44/04. Name of product manufacturer BAR code Unique number allocated to your specific seat, for testing and tracking.

To determine if a child car seat fits your car, there are 3 types of car seat approvals:

Universal approval

The seat is approved for use in all vehicles that meet ECE R14 and R16 regulations. Any Isofix car seat must use the Isofix anchorage points including the top tether or foot support and the vehicle’s handbook must state that the car is suitable for “Universal Isofix child seats”.

Semi-universal approval

Semi-universal approval is when, in addition to the standard requirements, other safety devices for attaching a seat are used and require additional testing. For example: some vehicles provide additional storage space within or beneath the floor area that can influence the behavior of a child seat foot support, therefore you need to check the child seat manufacturer’s car fitting list for your car type and model.

Vehicle specific approval

The child seat is tested in an additional car-specific dynamic crash test and approved only for these cars. The car must be listed in the child seat manufacturer’s car fitting list. This may include special features or designs that can only be installed in a car of a specific type.

i-Size (ECE R129)

i-Size is a new regulation for child car seats that will run in parallel to the current regulation (ECE R44/04) for the next few years. It has been in force since July 9th 2013. We were a major contributor to its development and believe that it will greatly increase protection for little ones across Europe.

The key changes are:

Extended rearward facing travel until a minimum of 15 months Proven to be the safer way to travel in case of frontal collisions

Added side impact test To ensure the seat provides better protection in the case of side collisions

ISOFIX only seats Using our 1997 invention together with Volkswagen to greatly reduce the risk of incorrect installation

Based on the age and size of the child rather than weight Reflecting the latest safety data and giving parents a clearer indicator of what seat is right for their child and when their child is ready to be moved to the next stage car seat.

i-Size (or ECE R129) approved car seats can be recognized on the orange approval label by the “i-Size” indication. Additionally, one can easily find the appropriate length classification of the car seat on the label. The remainder of the approval label looks alike the ECE R44 label.

Nearly 50 years of experience and constant technical innovation have enabled us to understand in minute detail what happens in different types of collisions. Based on our continually developing knowledge, a 5-point harness system is the only form of restraint we use on all of our Group 0+/1, 1 and Group 1/2 car seats – and we are increasingly finding ways to build extended 5-point harnessing into our Group 2 seats.


In Group 0 and 0+ children are generally restrained with a 3- or 5-point harness.

In Group 1 children are restrained either with the 5-point harness or the shield system (also referred to as safety cushion, impact shield, tray shield).

In Group 2 and 3 children are commonly restrained with an adult seat belt. However we are also working to champion extended 5-point harnessing for Group 2 so that children can benefit from the safety of 5-point harnesses for longer.


A 5-point harness significantly decreases the forces a child experiences during a crash since the forces are diverted from the child along the harnessing to the five points of contact with the seat. When the child is decelerated by the harness, the cushioning occurs across a wide area and limits shoulder and hip movements, resulting in low stress to the spine and the forces being directed away from the parts of the body containing vital organs.

In case of a roll-over, side impact or an offset impact (where combined vertical, lateral and or oblique loading lateral forces can lead to ejection or submarining), the shoulder contact points and the crotch strap stop those risks and keep the child safely in the protecting seat shell.

In addition, the harness allows for adjustment to the child’s body and therefore offers a good and customised fit.


In all 5-point harness seats, the straps come down over the shoulders and across the hips to fasten to the buckle that comes up between the legs. The harness sits closely against the bony parts of the pelvis (the crotch and hip straps) and across the shoulders and rib cage (the shoulder straps). When a child moves forward in the seat, as they would in a crash, the properly tightened harness is already "holding" the child and it effectively restrains them, spreading the crash forces out through the seat and the remaining forces across the strong bones of the body.


Harnesses are complex to design. The visible part is only a small fraction of the total harnessing system, which comprises straps, tongues, crotch strap, attachment means to the shell and a key element: the buckle. Technology is needed to allow easy tightening and release of the harness, and the harness needs to be routed around the shell to allow connection at the right points for the load to be distributed whilst providing easy access to the parents securing their child in the seat. In addition, designing a shell which can properly withstand the forces the harness places on the upper shell, to effectively restrain the upper body, is technically advanced and costly.

Booster cushions and highback booster seats are not the same. It is our belief, based on our decades of experience and our continuing research that normal booster cushions simply don’t offer adequate side impact or head protection. That’s why we only sell highback booster seats. That’s why we have worked to create Europe’s first Group 2/3 seat with a ‘Very Good’ safety rating.*

*Stiftung Warentest and ADAC Motorwelt, 11/2013, for the KIDFIX XP SICT when used with ISOFIX

Booster cushions offer:

no side or head protection no guidance to ensure that seat belts are correctly positioned and fitted.

Our KID range of highback booster seats offers:

  • deep, softly padded full side wings
  • height adjustable headrest and belt guide
  • V-shaped backrest to ensure a perfect fit throughout your child’s development
  • Intuitively positioned seat belt guides enter

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Typical booster cushion protection area Ordinary highback booster protected area Britax KID Range protected area

We are not alone in our belief that booster cushions are not the safest option for your child

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Booster cushions are still sold because it is not required by current EU safety standards to conduct tests for side collisions, however if the regulations change, we do not believe that any new booster cushions would pass. Parents are also sometimes unaware that Booster cushions offer no head support in the event of a side impact crash. But here at BRITAX we design our products to provide protection during traffic collisions from every angle of impact.

We believe that risks shouldn’t be taken when it comes to child safety. A second-hand car seat with an unknown history is always a risk as you cannot be sure that it hasn’t been involved in an accident (even if there are no visual signs of damage).

American child seats are approved according to the US standard FMVSS 230. In Europe, child seats must conform to the European safety standards ECE R44/04 or ECE R129. Therefore we always recommend that parents choose only car seats that conform to the European standards for use in Europe.

The function of the vehicle seatbelt in a Group 2/3 child car seat (Britax KIDFIX II XP (SICT), KIDFIX XP (SICT), KIDFIX SL (SICT), KID II, DISCOVERY SL and ADVENTURE) is to hold it and the child firmly and properly in place. Insufficient (incomplete) seatbelt retracts can be a common issue with Group 2/3 child car seats. There are many factors that contribute to this including the temperature outdoors and in the car, as well as the angle of the vehicle seatbelt as it goes through the upper belt guide of the child car seat. Since the upper point at which a car’s seatbelt connects to the body of the car is not the same in all cars, the result varies case by case depending on car type, child car seat, headrest position and other circumstances. Upon purchasing the child car seat, it is important to do an installation test. Please also try to ensure that the vehicle seatbelt retracts sufficiently when your child is sitting in the child car seat.

To determine if you have an issue, please check the vehicle seatbelt retraction when using the Group 2/3 child seat.

Checking your child car seat:

Please always follow the user guide of the car seat (incl. type lists if applicable) and car for the installation of the child car seat.

1) When your child is sitting in the child car seat, make sure that the vehicle seatbelt runs smoothly and securely through the upper belt guide and lower belt guide.

2 ) It is important that the vehicle seatbelt fits snugly and consistently against the body of the child so that it keeps the child and child safety seat securely in place. Always make sure the seatbelt is properly fastened and ensure that it is not twisted.

3) Once the child has been seated, ask your child to lean forward and then back in the child car seat. Should you notice that the vehicle seatbelt does not retract fully and there is a slack in the seatbelt, please try the following:

  • Adjust the headrest of the child car seat so that the headrest is, where possible, 1-2 slots higher or lower (subject to the height of the child and additional guidance in the user manual) than its previous position.
  • If the belt-retract is still insufficient and the child car seat has an XP-PAD, please test the belt-retract without using the XP-PAD. If the seatbelt sufficiently retracts without the XP-PAD, then the child car seat should be used without the XP-PAD. Even without the XP-PAD, the child car seat still provides superior safety performance.
  • Should these steps not solve the issue, then please do not use this car seat and contact Britax customer service immediately.
  • If the vehicle seatbelt remains properly in place when your child moves around while seated, but does not fully retract when your child climbs out of the car, then you can use the child car seat without any restrictions.

All Britax infant carriers are compatible with all Britax and Britax BOB pushchairs. They are also compatible with the below models from other leading pushchair brands.

More information on compatible pushchairs

Please ask trained store staff for the required adaptors and do contact the pushchair manufacturer if you have any further questions.

The following Britax models have been approved for use on a plane:

  • BABY-SAFE plus
  • BABY-SAFE plus II
  • BABY-SAFE plus SHR II TÜV ID number 9811400300 (ECE approval no. 03301146 or 04301146)

Suitable for children up to 13kg, or until the head extends over the edge of the infant carrier. The label certifying suitability for airline use can be found on the car seat.

  • ECLIPSE TÜV ID number 0000028802 (ECE approval no. 040149)

Suitable for children from 9 to18 kg. This model is approved for airline use subject to airline regulations. Accessory Kits is necessary and available from your dealer.

As airline regulations regarding suitable car seats can change regularly, we recommend that you always check with your airline before travelling.

Sweating in young babies can often be a sign that their ability to thermo regulate is still developing. We advise that parents use their judgement in terms of how their child is dressed if they appear to be hot. However we also offer specific summer accessories for some of our car seats. Please do check our accessories section for further details.

The design of car interiors can effect the angle at which a car seat fits – and therefore the angle at which the child rests within the seat. In designing every seat our goal is the optimal balance between safety and comfort. The steeper the angle of the back of the infant carrier, the greater the protection in the event of an accident. The flatter the baby is in the shell, the easier it is for a young child with developing neck muscles, but the safety systems of the seat may no longer be working at optimum capacity. We generally advise that consumers seek advice from qualified personnel when buying and fitting a child seat. If a qualified car seat fitter judges that the angle of the shell is too steep in conjunction with the vehicle seat, then for Britax seats you can request a free inclination adapter – either through your retailer or by contacting our Customer Service Department. This adapter is very easy to install using the supplied manual.

In designing our restraint systems we aim to strike a delicate balance in terms of the forces needed to open a buckle – high enough to deter children from opening it themselves, but not so high that the buckle can’t be opened by someone else in case of a dangerous accident situation. Equally a more complicated lock system is not legally permitted if it could also prevent an adult being able to open the buckle in an emergency.

In terms of harnessing, we recommend that parents find the best balance between tightening the harness so tautly that the child is uncomfortable and tries to escape from it – and tightening it so loosely that it is easy for the child simply to slide out of the harness. The harness should be a tight fit but without tension against the body (two fingers should be able to fit between the harness and the child's chest). If your child unbuckles or slips out of his harness we recommend that you stop immediately and re-harness your child.

After an accident in which a car seat had been involved, we strongly recommend that the seat is replaced if involved in an accident at speeds of 10 kmph or more as the forces absorbed by the seat could lead to fine cracks in the structure (which may not be visible to the eye).

Infant carriers from Group 0/0+ must be fastened in a rearward facing direction. These seats should not be used in conjunction with an airbag on the passenger seat. The same applies to our Group 0+/1 and Group 1/2 products such as FIRST CLASS PLUS, MAX-FIX II, DUALFIX when in rearward facing mode, MAX-WAY and MULTI-TECH II – however for MAX-FIX II and DUALFIX, they can only be used in cars that also have ISOFIX connection on the front seat. Please refer to your car seat and vehicle instruction manuals.

Britax car seats in Groups 1 and 2-3 can be used in principle in the passenger seat. The same applies to our Group 0+/1 products such as FIRST CLASS PLUS and DUALFIX when in forward facing mode. However, it is advisable to move the front passenger seat as far back as possible if a passenger airbag is activated. Please refer to your car seat and vehicle instruction manuals. In general, children should be transported on the rear seats as much as possible where there is less risk of injury in case of an accident.

Unlike the front airbag on the passenger side, the side airbags only inflate a small amount – so they have minimal contact with the child car seat. As long as a child is properly secured within the car seat and cannot lean out if it, the use of a car side airbag does not pose a risk.

If you are concerned, we advise that you contact the vehicle manufacturer to ask how far the side airbags come out if they deploy and whether they are likely to contact a child restraint in the rear outboard seats. EuroNCAP tests include assessing the safety of child seats in a side impact, so check to see if your vehicle model is one of those that has been tested.

If a child is wearing a very thick coat, there is a risk that the harness or car seat belts cannot be tightened to sufficient tension. So we would recommend in general that very thick coats are removed in the car and the child is covered with a blanket over the top of the harness if extra warmth is needed.

We offer a guarantee for manufacturing or material defects on all products for two years. The warranty period begins on the date of purchase. Please retain your receipt as proof of purchase and complete your warranty card if available. For any warranty enquiries please contact the retailer where you purchased your seat.

The cover can be removed and washed with mild detergent on a gentle 30 °C cycle. Please follow the instructions on the washing label of the cover. Do not place on a spin cycle and do not place in a tumble dryer.

For instruction manuals for our current models, please visit our Product Support section.

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