Theorem pm3.21

Description: Join antecedents with conjunction. Theorem *3.21 of WhiteheadRussell p. 111. (Contributed by NM, 5-Aug-1993)

	Ref	Expression
Assertion	pm3.21	$$⊢\phi \to \left(\psi \to \left(\psi \wedge \phi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		id	$$⊢\left(\psi \wedge \phi \right)\to \left(\psi \wedge \phi \right)$$
2	1	expcom	$$⊢\phi \to \left(\psi \to \left(\psi \wedge \phi \right)\right)$$