Theorem dfsb

Description: Simplify definition df-sb by removing its provable hypothesis. (Contributed by Wolf Lammen, 5-Feb-2026)

	Ref	Expression
Assertion	dfsb	|- ( [ t / x ] ph <-> A. y ( y = t -> A. x ( x = y -> ph ) ) )

Proof

Step	Hyp	Ref	Expression
1		sbjust	|- ( A. y ( y = t -> A. x ( x = y -> ph ) ) <-> A. z ( z = t -> A. x ( x = z -> ph ) ) )
2	1	df-sb	|- ( [ t / x ] ph <-> A. y ( y = t -> A. x ( x = y -> ph ) ) )