Theorem wl-impchain-a1-2

Description: Inference rule, a copy of a1d . First recursive proof based on the previous instance. (Contributed by Wolf Lammen, 20-Jun-2020) (New usage is discouraged.) (Proof modification is discouraged.)

	Ref	Expression
Hypothesis	wl-impchain-a1-2.a	$$⊢\phi \to \psi$$
Assertion	wl-impchain-a1-2	$$⊢\phi \to \left(\chi \to \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		wl-impchain-a1-2.a	$$⊢\phi \to \psi$$
2	1	wl-impchain-a1-1	$$⊢\chi \to \left(\phi \to \psi \right)$$
3	2	wl-impchain-com-1.2	$$⊢\phi \to \left(\chi \to \psi \right)$$