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Metamath Proof Explorer

Theorem idd

Description: Principle of identity id with antecedent. (Contributed by NM, 26-Nov-1995)

		Ref	Expression
	Assertion	idd	$⊢ φ \to (ψ \to ψ)$

Step	Hyp	Ref	Expression
1		id	$⊢ ψ \to ψ$
2	1	a1i	$⊢ φ \to (ψ \to ψ)$