intro hasn
case mp
x : String
a : State → ℕ
s t : State
⊢ (Stmt.assign x a, s) ⟹ t → t = State.update x (a s) s
case mp
x : String
a : State → ℕ
s t : State
hasn : (Stmt.assign x a, s) ⟹ t
⊢ t = State.update x (a s) s