Theorem sssneq 15646

Description: Any two elements of a subset of a singleton are equal. (Contributed by Jim Kingdon, 28-May-2024.)

Assertion

Ref	Expression
sssneq	|- ( A C_ { B } -> A. y e. A A. z e. A y = z )

Distinct variable groups:   y, A, z   y, B, z

Proof of Theorem sssneq

Step	Hyp	Ref	Expression
1		simpl 109	. . . . 5 |- ( ( A C_ { B } /\ ( y e. A /\ z e. A ) ) -> A C_ { B } )
2		simprl 529	. . . . 5 |- ( ( A C_ { B } /\ ( y e. A /\ z e. A ) ) -> y e. A )
3	1, 2	sseldd 3184	. . . 4 |- ( ( A C_ { B } /\ ( y e. A /\ z e. A ) ) -> y e. { B } )
4		elsni 3640	. . . 4 |- ( y e. { B } -> y = B )
5	3, 4	syl 14	. . 3 |- ( ( A C_ { B } /\ ( y e. A /\ z e. A ) ) -> y = B )
6		simprr 531	. . . . 5 |- ( ( A C_ { B } /\ ( y e. A /\ z e. A ) ) -> z e. A )
7	1, 6	sseldd 3184	. . . 4 |- ( ( A C_ { B } /\ ( y e. A /\ z e. A ) ) -> z e. { B } )
8		elsni 3640	. . . 4 |- ( z e. { B } -> z = B )
9	7, 8	syl 14	. . 3 |- ( ( A C_ { B } /\ ( y e. A /\ z e. A ) ) -> z = B )
10	5, 9	eqtr4d 2232	. 2 |- ( ( A C_ { B } /\ ( y e. A /\ z e. A ) ) -> y = z )
11	10	ralrimivva 2579	1 |- ( A C_ { B } -> A. y e. A A. z e. A y = z )

Syntax hints:   -> wi 4   /\ wa 104   = wceq 1364   e. wcel 2167   A.wral 2475   C_ wss 3157   {csn 3622

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-io 710  ax-5 1461  ax-7 1462  ax-gen 1463  ax-ie1 1507  ax-ie2 1508  ax-8 1518  ax-10 1519  ax-11 1520  ax-i12 1521  ax-bndl 1523  ax-4 1524  ax-17 1540  ax-i9 1544  ax-ial 1548  ax-i5r 1549  ax-ext 2178

This theorem depends on definitions:  df-bi 117  df-tru 1367  df-nf 1475  df-sb 1777  df-clab 2183  df-cleq 2189  df-clel 2192  df-nfc 2328  df-ral 2480  df-v 2765  df-in 3163  df-ss 3170  df-sn 3628

This theorem is referenced by: (None)