Require Export bbv.Nomega.
Set Implicit Arguments.
Fixpoint mod2 (n : nat) : bool :=
match n with
| 0 => false
| 1 => true
| S (S n') => mod2 n'
end.
Ltac rethink :=
match goal with
| [ H : ?f ?n = _ |- ?f ?m = _ ] => replace m with n; simpl; auto
end.

Theorem mod2_S_double : forall n, mod2 (S (2 * n)) = true.