a b c : ℕ,
H : c = b
⊢ ℕ

a b c : ℕ,
H : c = b,
v : ℕ := ?m_1
⊢ a + c = a + b
------------
a b c : ℕ,
H : c = b,
v : ℕ := a + b
⊢ a + c = a + b
------------
a c : ℕ,
v : ℕ := a + c
⊢ a + c = a + c