symmetricDifferece probadorCollection

idem #48

symmetricDifference idem  invariantsubOrderedSet0 invariantSubOrderedSet01a


Context C
invariantSymmetricDifference0a : OrderedSet{'b', 'a', 'b', 'c'}->symmetricDifference(Set{'a', 'c', 'd'})=Set{'d', 'b'}
FAIL

Context C
invariantSymmetricDifference0b : OrderedSet{'b', 'a', 'b', 'c'}->symmetricDifference(Set{'a', 'c', 'd'})->size()=0
OK


sin embargo
Context C
invariantSymmetricDifference1a : Set{'b', 'a', 'b', 'c'}->symmetricDifference(Set{'a', 'c', 'd'})=Set{'d', 'b'}
OK
funciona como se espera