Definition bool_fun_neg (bf : bool_fun) : bool_fun :=
  fun vb : var_binding => negb (bf vb).Definition bool_fun_or (bf1 bf2 : bool_fun) : bool_fun :=
  fun vb : var_binding => bf1 vb || bf2 vb.

Lemma bool_fun_neg_one : bool_fun_neg bool_fun_one = bool_fun_zero.