(* ndestrcut does not work *)
ntheorem not_eq_true_false : true \neq false.
-#Heq; nchange with match true with [true ⇒ False|false ⇒ True];
+napply nmk; #Heq;
+nchange with match true with [true ⇒ False|false ⇒ True];
nrewrite > Heq; //; nqed.
ndefinition notb : bool → bool ≝
[ true ⇒ P
| false ⇒ Q].
+(*
+ntheorem fff: false ≠ true.
+/2/;
+//; nqed. *)
+
ntheorem bool_to_decidable_eq:
∀b1,b2:bool. decidable (b1=b2).
#b1; #b2; ncases b1; ncases b2; /2/;
-@2;/2/; nqed.
+@2;/3/; nqed.
ntheorem true_or_false:
∀b:bool. b = true ∨ b = false.