Axiom ax-frege58b

Description: If A. x ph is affirmed, [ y / x ] ph cannot be denied. Identical to stdpc4 . Axiom 58 of Frege1879 p. 51. (Contributed by RP, 28-Mar-2020) (New usage is discouraged.)

	Ref	Expression
Assertion	ax-frege58b	$$⊢\forall x\phi \to \left[y/x\right]\phi$$

Detailed syntax breakdown

Step	Hyp	Ref	Expression
0		vx	$$setvarx$$
1		wph	$$wff\phi$$
2	1 0	wal	$$wff\forall x\phi$$
3		vy	$$setvary$$
4	1 0 3	wsb	$$wff\left[y/x\right]\phi$$
5	2 4	wi	$$wff\left(\forall x\phi \to \left[y/x\right]\phi \right)$$