fact: Definition move (s1 s2 : state) := s2 = rright s1 \/ s2 = rright (rright s1) \/ s2 = rright (rright (rright s1)) \/ s2 = rback s1 \/ s2 = rback (rback s1) \/ s2 = rback (rback (rback s1)) \/ s2 = rdown s1 \/ s2 = rdown (rdown s1) \/ s2 = rdown (rdown (rdown s1)).
imports: ZArith List