apply And.intro
case mp
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n m : ℕ
x✝ : n < m
this : step n ≤ m
k : ℕ
h✝ : step n + k ≃ m
⊢ Positive (step k) ∧ m ≃ n + step k
case mp.left
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n m : ℕ
x✝ : n < m
this : step n ≤ m
k : ℕ
h✝ : step n + k ≃ m
⊢ Positive (step k)

case mp.right
ℕ : Type
inst✝³ : Core ℕ
inst✝² : Induction ℕ
inst✝¹ : Addition ℕ
inst✝ : Sign ℕ
order_inst : Order ℕ
n m : ℕ
x✝ : n < m
this : step n ≤ m
k : ℕ
h✝ : step n + k ≃ m
⊢ m ≃ n + step k