diff --git a/tests/lean/run/class4.lean b/tests/lean/run/class4.lean
new file mode 100644
index 000000000..2ea45df96
--- /dev/null
+++ b/tests/lean/run/class4.lean
@@ -0,0 +1,95 @@
+import standard
+
+inductive nat : Type :=
+| zero : nat
+| succ : nat → nat
+
+definition add (x y : nat)
+:= nat_rec x (λ n r, succ r) y
+
+infixl `+`:65 := add
+
+theorem add_zero_left (x : nat) : x + zero = x
+:= refl _
+
+theorem add_succ_left (x y : nat) : x + (succ y) = succ (x + y)
+:= refl _
+
+definition is_zero (x : nat)
+:= nat_rec true (λ n r, false) x
+
+theorem is_zero_zero : is_zero zero
+:= eqt_elim (refl _)
+
+theorem not_is_zero_succ (x : nat) : ¬ is_zero (succ x)
+:= eqf_elim (refl _)
+
+theorem dichotomy (m : nat) : m = zero ∨ (∃ n, m = succ n)
+:= nat_rec
+     (or_intro_left _ (refl zero))
+     (λ m H, or_intro_right _ (exists_intro m (refl (succ m))))
+     m
+
+theorem is_zero_to_eq (x : nat) (H : is_zero x) : x = zero
+:= or_elim (dichotomy x)
+     (assume Hz : x = zero, Hz)
+     (assume Hs : (∃ n, x = succ n),
+       exists_elim Hs (λ (w : nat) (Hw : x = succ w),
+         absurd_elim _ H (subst (symm Hw) (not_is_zero_succ w))))
+
+theorem is_not_zero_to_eq {x : nat} (H : ¬ is_zero x) : ∃ n, x = succ n
+:= or_elim (dichotomy x)
+     (assume Hz : x = zero,
+       absurd_elim _ (subst (symm Hz) is_zero_zero) H)
+     (assume Hs, Hs)
+
+theorem not_zero_add (x y : nat) (H : ¬ is_zero y) : ¬ is_zero (x + y)
+:= exists_elim (is_not_zero_to_eq H)
+     (λ (w : nat) (Hw : y = succ w),
+        have H1 : x + y = succ (x + w), from
+          calc x + y = x + succ w   : {Hw}
+                 ... = succ (x + w) : refl _,
+        have H2 : ¬ is_zero (succ (x + w)), from
+          not_is_zero_succ (x+w),
+        subst (symm H1) H2)
+
+inductive not_zero (x : nat) : Bool :=
+| not_zero_intro : ¬ is_zero x → not_zero x
+
+theorem not_zero_not_is_zero {x : nat} (H : not_zero x) : ¬ is_zero x
+:= not_zero_rec (λ H1, H1) H
+
+class not_zero
+
+theorem not_zero_add_right [instance] (x y : nat) (H : not_zero y) : not_zero (x + y)
+:= not_zero_intro (not_zero_add x y (not_zero_not_is_zero H))
+
+theorem not_zero_succ [instance] (x : nat) : not_zero (succ x)
+:= not_zero_intro (not_is_zero_succ x)
+
+variable div : Π (x y : nat) {H : not_zero y}, nat
+
+variables a b : nat
+
+check div a (succ b)
+check (λ H : not_zero b, div a b)
+check (succ zero)
+check a + (succ zero)
+check div a (a + (succ b))
+
+exit
+
+inductive not_zero : nat → Bool :=
+| not_zero_intro : Π (x : nat), not_zero (succ x)
+
+class not_zero
+instance not_zero_intro
+
+
+theorem not_zero (x : nat) (H : not_zero x) :  →
+
+exit
+
+
+axiom add_not_zero : ∀ {x y : nat}, not_zero x → not_zero y → not_zero (x + y)
+