---

       # MATH introduce sugar for let
       # if would be good to introduce desugarings more rigorously, but for now...
       # ... just a very vague sketch
[hear] (intro let);

[hear] (= (let ((x 10)) (+ (x) 5))
           ((? x / + (x) 5) 10));

[hear] (= (let ((x 10) (y 5)) (+ (x) (y)))
           (((? x / ? y / + (x) (y)) 10) 5));