// postfix order per statement: operands by name, then operators.
// binary operators are left associative; unary operators nest rightwards
6: a a b c * +
7: a a b - c -
8: a a b / c /
9: a a b + c *
10: a a neg b *
11: a a neg neg
12: d d not d and
13: d d d d and or
14: d a b < d =
15: d a b = a c <> d not and or
16: a a b * c a * + b c / -
17: d a b + c a * <
18: d a b <= a c >= or
19: a b + c neg *
20: a a b c - -