Description: Existence of a class abstraction of existentially restricted sets. The
class B can be thought of as an expression in x (which is
typically a free variable in the class expression substituted for
B ) and the class abstraction appearing in the statement as the
class of values B as x varies through A . If the "domain"
A is a set, then the abstraction is also a set. Therefore, this
statement is a kind of Replacement. This can be seen by tracing back
through the path axrep6g , axrep6 , ax-rep . See also
abrexex2g . There are partial converses under additional conditions,
see for instance abnexg . (Contributed by NM, 3-Nov-2003)(Proof
shortened by Mario Carneiro, 31-Aug-2015) Avoid ax-10 , ax-11 ,
ax-12 , ax-pr , ax-un and shorten proof. (Revised by SN, 11-Dec-2024)