In RERS challenges, file are written in C and
the environment is modelled by scanf("%d",...).

During the translation, this statement has been
converted into __RERS__ = __RERS__ + 1, since this
variable is only used to represents the environment.

As a consequence, the option -rers "1;2;3" will modify
the previous assignment in order to represent the
environment. In other this instruction will be replaced
by three assignment
   - __RERS__ = 1
   - __RERS__ = 2
   - __RERS__ = 3
while  the instruction __RERS__ = __RERS__ + 1 will be discarded

* boilerplate/main.go, main.go: Here.