n : Nat
h : n = 0
m : Nat := n + 1
v : Nat := m + 1
this : v = n + 2
⊢ 0 + n = 0
m : Nat := 0 + 1
v : Nat := m + 1
this : v = 0 + 2
⊢ 0 + 0 = 0