Branch :
1 + 20 21 1 + 20 / 3 7 to_lisp(quote 1 + 20 / 3) [+, 1, [/, 20, 3]] 1 + 20 / 3 * 4 25 to_lisp(quote 1 + 20 / 3 * 4) [+, 1, [*, [/, 20, 3], 4]] 1 + 20 / 3 * 4 - 5 20 to_lisp(quote 1 + 20 / 3 * 4 - 5) [-, [+, 1, [*, [/, 20, 3], 4]], 5] 20 / 3 * 4 - 5 19 to_lisp(quote 20 / 3 * 4 - 5) [-, [*, [/, 20, 3], 4], 5] (1 + 20) 21 to_lisp(quote (1 + 20)) [_"()", [+, 1, 20]] a = (1 + 20) 21