apply Nat.le_add_right
case a
a b y x : ℕ
⊢ a ≤ a + b

case h
a b y x : ℕ
⊢ (x + 1) ^ a ≤ (x + 1) ^ (a + b)

case h
a b y x : ℕ
⊢ (x + 1) ^ a ≤ (x + 1 + y) ^ a
case h
a b y x : ℕ
⊢ (x + 1) ^ a ≤ (x + 1) ^ (a + b)

case h
a b y x : ℕ
⊢ (x + 1) ^ a ≤ (x + 1 + y) ^ a