Indeed, it is standard, but eliding the parentheses doesn't mean they aren't implicitly there, and doesn't turn non-associativity into non-commutativity. Commut

Indeed, it is standard, but eliding the parentheses doesn't mean they aren't implicitly there, and doesn't turn non-associativity into non-commutativity. Commutivity means that these are equal: (((b + s) + s) + s) + s == s + (s + (s + (s + b)))