Backward Propagation

Backward Propagation
Identifier:	East 3-7
Area:	Eastern Wetlands
Puzzle Type:	Main
Previous Puzzle:	Hidden
Next Puzzle:	Positional Interchange

Backward Propagation is the seventh main puzzle in the Eastern Wetlands area of The Talos Principle 2.

Puzzle elements

• Blue door
• Emitter
• Inverter
• Pressure plate
• Purple barrier
• Receiver

Overview

When you enter the puzzle, you find yourself in the outer room with a red emitter and an inverter. To the left, a little bit inside, is the progress wheel, access to which is controlled by a blue receiver. On the right is a pressure plate, which controls the blue door to a narrow strip. There, we see a red receiver, immediately followed by a purple barrier. Behind the barrier is a large rear room. In the middle of the room, we see another inverter, and to the right is a red receiver which blocks off access to a blue emitter.

Hints

A basic hint:

[ hint ]

Since the name of the puzzle is Backward Propagation, you have to solve the puzzle from the back to the front.

If you're having trouble getting started:

[ hint ]

Try to figure out what the pressure plate does. You can hold it down with the inverter for now, but you should let the inverter do other useful things soon.

If you're having trouble figuring out what an intermediate step should be:

[ hint ]

Try to get the blue emitter in the inner room open.

If you're wondering what the middle blue receiver does (the one in the little strip):

[ hint ]

It keeps the blue door open. Nothing can turn off a purple barrier.

If you're having trouble keeping the middle door open:

[ hint ]

The outer inverter can pull double duty, so that the pressure plate becomes irrelevant.

Solution

[ solution ]

• 
  Take the first inverter and place it down on the pressure plate.
• 
  Take the second inverter, connect the blue emitter to the red receiver.
• 
  Take the first inverter, connect the red emitter to the second inverter through the door.
• 
  Position yourself on the pressure plate until you hear the red receiver activate.
• 
  Take the first inverter again and connect it to the second inverter, as well as both blue receivers.
• 
  Position yourself on the pressure plate again and wait until both blue receivers activate.

Trivia and glitches

• The name Backward Propagation is a reference to a very famous algorithm used in machine learning, Backpropagation.