Theorem sb10f 2122

Description: Hao Wang's identity axiom P6 in Irving Copi, Symbolic Logic (5th ed., 1979), p. 328. In traditional predicate calculus, this is a sole axiom for identity from which the usual ones can be derived. (Contributed by NM, 9-May-2005.) (Revised by Mario Carneiro, 6-Oct-2016.)

Hypothesis

Ref	Expression
sb10f.1	|- F/xph

Assertion

Ref	Expression
sb10f	|- ([y / z]ph <-> E.x(x = y /\ [x / z]ph))

Distinct variable group:   x,y

Allowed substitution hints:   ph(x,y,z)

Proof of Theorem sb10f

Step	Hyp	Ref	Expression
1		sb10f.1	. . . 4 |- F/xph
2	1	nfsb 2109	. . 3 |- F/x[y / z]ph
3		sbequ 2060	. . 3 |- (x = y -> ([x / z]ph <-> [y / z]ph))
4	2, 3	equsex 1962	. 2 |- (E.x(x = y /\ [x / z]ph) <-> [y / z]ph)
5	4	bicomi 193	1 |- ([y / z]ph <-> E.x(x = y /\ [x / z]ph))

Syntax hints:   <-> wb 176   /\ wa 358  E.wex 1541   F/wnf 1544  [wsb 1648

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925

This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649

This theorem is referenced by: (None)