element		( element ), <number>, "<string>", set, assignment, test, size
set		( set ) { element, ... }, var, assignment, set operation

(tests, result is 0 if false, 1 if true)
subset		S1 <= S2
proper subset	S1 < S2
equal		S1 = S2
not equal	S1 != S2
is in set 	e [ S
is not in set	e ![ S

(set operations, result is set)
union		S1 + S2
intersection	S1 ^ S2
difference	S1 - S2
symmetric diff	S1 / S2
powerset	@ S

assignment	var : element

(operations, result is number)
size		|S|