Using FOL
		The set domain: n s Set(s)  (s = {} )  (x,s2 Set(s2)  s = {x|s2}) n x,s {x|s} = {} n x,s x  s  s = {x|s} n x,s x  s  [ y,s2} (s = {y|s2}  (x = y  x  s2))] n s1,s2 s1  s2  (x x  s1  x  s2) n s1,s2 (s1 = s2)  (s1  s2  s2  s1) n x,s1,s2 x  (s1  s2)  (x  s1  x  s2) n x,s1,s2 x  (s1  s2)  (x  s1  x  s2)