OFFSET
1,2
COMMENTS
These universes need not satisfy the Power Set Axiom.
EXAMPLE
1 entity = 1 universe that consists of the empty set. 2 entities = 2 universes: when a = {{}}, when a = {a} on the other hand. 3 entities = 6 universes: a = {{}}, b = {a}; a = {{}}, b = {b}; and so on. 4 entities = 60 universes...
CROSSREFS
KEYWORD
hard,nonn,nice,more
AUTHOR
Csabay Karoly (csabay58(AT)gmail.com), Feb 19 2009, Jun 14 2009, Mar 20 2010
STATUS
approved