Description: Define the collection of "GCH-sets", or sets for which the generalized
continuum hypothesis holds. In this language the generalized continuum
hypothesis can be expressed as GCH =V . A set x satisfies the
generalized continuum hypothesis if it is finite or there is no set
y strictly between x and its powerset in cardinality. The
continuum hypothesis is equivalent to om e. GCH . (Contributed by Mario Carneiro, 15-May-2015)