environment: send this letters: AEAEAEAEAEAE it changes letter when an ack is
recieved.
environment2: send any letter it changes letter when an ack is
recieved.
encoder : read the new letter only when valid is true and send an acknowledge
when it's done transmitting the character's code.

protect_env.reg : the set of environment register to be protected.
env.fair : the fairness contraint for environnment2

rob_composition.v : the composoiton golden/faulty/env
env+huff.v : the composition of Huffman and environment