1a) The set {3, 3, {3}} has 2 elements, since we do not count repeated elements and 3 ¹ {3}.
b) Yes, {1,1,2} = {1,2} since we do not count repeated
elements.
c) Yes, 1 Î
{1}.
d) No. 1 is not in the set {{1}}, since {{1}} has only one
element and that is the set containing 1.