Theorem dfvd1impr

Description: Right-to-left part of definition of virtual deduction. (Contributed by Alan Sare, 21-Apr-2011) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	dfvd1impr	$$⊢\left(\phi \to \psi \right)\to \left(\phi \to \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		df-vd1	$$⊢\left(\phi \to \psi \right)\leftrightarrow \left(\phi \to \psi \right)$$
2	1	biimpri	$$⊢\left(\phi \to \psi \right)\to \left(\phi \to \psi \right)$$