@neauoire That's a big divergence from most Lisps, I think. They only look for a function at the head of a list. Without quote they'd resolve a symbol later in the list to its value but wouldn't try to execute it.

The very first bit of code shown in SICP (so Scheme) is (+ 137 349).

E.g., (MUL (QUOTE 2) (ADD (QUOTE 1) X)) could be more-simply written as (MUL 2 (ADD 1 X)) with the same effect.