Theorem nfeu 2033

Description: Bound-variable hypothesis builder for existential uniqueness. Note that 𝑥 and 𝑦 needn't be distinct. (Contributed by NM, 8-Mar-1995.) (Revised by Mario Carneiro, 7-Oct-2016.) (Proof rewritten by Jim Kingdon, 23-May-2018.)

Hypothesis

Ref	Expression
nfeu.1	⊢ Ⅎ𝑥𝜑

Assertion

Ref	Expression
nfeu	⊢ Ⅎ𝑥∃!𝑦𝜑

Proof of Theorem nfeu

Dummy variable 𝑧 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		nfv 1516	. . 3 ⊢ Ⅎ𝑧𝜑
2	1	sb8eu 2027	. 2 ⊢ (∃!𝑦𝜑 ↔ ∃!𝑧[𝑧 / 𝑦]𝜑)
3		nfeu.1	. . . 4 ⊢ Ⅎ𝑥𝜑
4	3	nfsb 1934	. . 3 ⊢ Ⅎ𝑥[𝑧 / 𝑦]𝜑
5	4	nfeuv 2032	. 2 ⊢ Ⅎ𝑥∃!𝑧[𝑧 / 𝑦]𝜑
6	2, 5	nfxfr 1462	1 ⊢ Ⅎ𝑥∃!𝑦𝜑

Syntax hints:  Ⅎwnf 1448  [wsb 1750  ∃!weu 2014

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-io 699  ax-5 1435  ax-7 1436  ax-gen 1437  ax-ie1 1481  ax-ie2 1482  ax-8 1492  ax-10 1493  ax-11 1494  ax-i12 1495  ax-bndl 1497  ax-4 1498  ax-17 1514  ax-i9 1518  ax-ial 1522  ax-i5r 1523

This theorem depends on definitions:  df-bi 116  df-tru 1346  df-nf 1449  df-sb 1751  df-eu 2017

This theorem is referenced by:  hbeu  2035  eusv2nf  4434