:: Some Basic Properties of Many Sorted Sets :: by Artur Korni{\l}owicz :: :: Received September 29, 1995 :: Copyright (c) 1995-2021 Association of Mizar Users
for I being set for x1, x2, X being ManySortedSet of I st ( for x being ManySortedSet of I holds ( x in X iff ( x = x1 or x = x2 ) ) ) holds X ={x1,x2}