Sergio Sánchez

https://github.com/mk12/sicp/blob/6213929f1c848d36551e40889bd2886e1dbaca4a/src/sicp/chapter-2.ss#L1111 I think the operation must be both associative and commutative. Commutativity is needed since fold-left corresponds to nested `(op prev-values-acc curr-el)` calls, that is ```(left-fold op init (1 2...