+ (((neg true) 10) 20)
+
+evaluates to 20, and
+
+ (((neg false) 10) 20)
+
+evaluates to 10.
+
+* Define an "and" operator.
+
+* Define an "xor" operator.
+
+(If you haven't seen this term before, here's a truth table:
+
+ true xor true = false
+ true xor false = true
+ false xor true = true
+ false xor false = false