simp
case refl
f : Bool → Bool → Bool
f_stable : f false false = false
m : Nat
hm : ¬m = 0
⊢ (if 0 = 0 then if f true false = true then m % 2 else 0
    else if f (decide (m % 2 = 1)) (decide (0 % 2 = 1)) = true then 1 % 2 else 0) =
    if f (decide (m % 2 = 1)) (decide (0 % 2 = 1)) = true then 1 else 0
case refl
f : Bool → Bool → Bool
f_stable : f false false = false
m : Nat
hm : ¬m = 0
⊢ (if f true false = true then m % 2 else 0) = if f (decide (m % 2 = 1)) false = true then 1 else 0