Definition df-reu

Description: Define restricted existential uniqueness.

Note: This notation is most often used to express that ph holds for exactly one element of a given class A . For this reading F/_ x A is required, though, for example, asserted when x and A are disjoint.

Should instead A depend on x , you rather assert exactly one x fulfilling ph happens to be contained in the corresponding A ( x ) . This interpretation is rarely needed (see also df-ral ). (Contributed by NM, 22-Nov-1994)

	Ref	Expression
Assertion	df-reu	|- ( E! x e. A ph <-> E! x ( x e. A /\ ph ) )

Detailed syntax breakdown

Step	Hyp	Ref	Expression
0		vx	|- x
1		cA	|- A
2		wph	|- ph
3	2 0 1	wreu	|- E! x e. A ph
4	0	cv	|- x
5	4 1	wcel	|- x e. A
6	5 2	wa	|- ( x e. A /\ ph )
7	6 0	weu	|- E! x ( x e. A /\ ph )
8	3 7	wb	|- ( E! x e. A ph <-> E! x ( x e. A /\ ph ) )