Goal:
    z : Z  z0 : Z
  ============================
   ((z0 <= z)%Z \/ False -> (z0 <= z)%Z)


DEBUG:Going to execute:
match goal with
           | |- ?X1 -> ?X2 => intro
           | |- ~ _ => unfold not at 1; intro
           end
Level 0: Backtrace:

No matching clauses for match.