The axiom of Zermelo-Fraenkel set theory
which asserts the existence of a set containing all the natural numbers,
where
denotes exists, is the empty set, is logical AND,
means for
all, and
denotes "is an element of" (Enderton 1977). Following von Neumann, , , , , ....
denotes exists, 
is the empty set, 
is logical AND,
means for
all, and 
denotes "is an element of" (Enderton 1977). Following von Neumann, 
, 
, 
, 
, ....
