apply congrArg
m n : Nat
⊢ m / 2 + n / 2 + (m % 2 + n % 2) / 2 = m / 2 + n / 2 + if getBit (m &&& n) 0 = true then 1 else 0
case h
m n : Nat
⊢ (m % 2 + n % 2) / 2 = if getBit (m &&& n) 0 = true then 1 else 0