stackInSomeState : {l m : Level} {D : Set l} {t : Set m} (s : SingleLinkedStack D) -> Stack {l} {m} D {t}  ( SingleLinkedStack  D)
stackInSomeState s =  record { stack = s ; stackMethods = singleLinkedStackSpec }

push->push->pop2 : {l : Level} {D : Set l} (x y : D) (s : SingleLinkedStack D) -> pushStack (stackInSomeState s) x (\s1 -> pushStack s1 y (\s2 -> pop2Stack s2 (\s3 y1 x1 -> (Just x ≡ x1) ∧ (Just y ≡ y1))))
push->push->pop2 {l} {D} x y s = record {pi1 = refl ; pi2 = refl}