Instance TraverseVarIsIdentity_my_value_my_value : @TraverseVarIsIdentity my_value _ my_value _.
Instance TraverseVarIsIdentity_my_value_my_term : @TraverseVarIsIdentity my_value _ my_term _.

Lemma subst_MyVAbs:
forall v k t,
subst v k (MyVAbs t) = MyVAbs (subst (shift 0 v) (1 + k) t).