let x = 3, y = 5 in x + y
let x = 3 in let y = x + 1 in x*y
let x = 2, y = x + 3, z = 2y + x + 1 in z^3*x + y
:type let x = 2, y = x + 3, z = 2y + x + 1 in z^3*x + y
let x : N = 5 + 3 in x + x
:type let x : N = 5 + 3 in x + x