MODULE main
VAR
  x : -1..20;
  increment : process inc(x);
  reset : process res(x);
ASSIGN
  init(x) := 0;
SPEC
  AF(x = -1 )

MODULE inc(y)
ASSIGN
  next(y) :=  (y+1) mod 20;

MODULE res(y)
ASSIGN
  next(y) := -1 ;
JUSTICE running