Theorem ax9vsep 4105

Description: Derive a weakened version of ax-9 1519, where x and y must be distinct, from Separation ax-sep 4100 and Extensionality ax-ext 2147. In intuitionistic logic a9evsep 4104 is stronger and also holds. (Contributed by NM, 12-Nov-2013.) (Proof modification is discouraged.) (New usage is discouraged.)

Assertion

Ref	Expression
ax9vsep	|- -. A. x -. x = y

Distinct variable group:   x, y

Proof of Theorem ax9vsep

Step	Hyp	Ref	Expression
1		a9evsep 4104	. 2 |- E. x x = y
2		exalim 1490	. 2 |- ( E. x x = y -> -. A. x -. x = y )
3	1, 2	ax-mp 5	1 |- -. A. x -. x = y

Syntax hints:   -. wn 3   A.wal 1341   = wceq 1343   E.wex 1480

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-in1 604  ax-in2 605  ax-5 1435  ax-gen 1437  ax-ie1 1481  ax-ie2 1482  ax-4 1498  ax-ial 1522  ax-ext 2147  ax-sep 4100

This theorem depends on definitions:  df-bi 116  df-tru 1346  df-fal 1349

This theorem is referenced by: (None)