Theorem syl121anc

Description: Syllogism combined with contraction. (Contributed by NM, 11-Mar-2012)

	Ref	Expression
Hypotheses	syl3anc.1	$$⊢\phi \to \psi$$
	syl3anc.2	$$⊢\phi \to \chi$$
	syl3anc.3	$$⊢\phi \to \theta$$
	syl3Xanc.4	$$⊢\phi \to \tau$$
	syl121anc.5	$$⊢\left(\psi \wedge \left(\chi \wedge \theta \right)\wedge \tau \right)\to \eta$$
Assertion	syl121anc	$$⊢\phi \to \eta$$

Proof

Step	Hyp	Ref	Expression
1		syl3anc.1	$$⊢\phi \to \psi$$
2		syl3anc.2	$$⊢\phi \to \chi$$
3		syl3anc.3	$$⊢\phi \to \theta$$
4		syl3Xanc.4	$$⊢\phi \to \tau$$
5		syl121anc.5	$$⊢\left(\psi \wedge \left(\chi \wedge \theta \right)\wedge \tau \right)\to \eta$$
6	2 3	jca	$$⊢\phi \to \left(\chi \wedge \theta \right)$$
7	1 6 4 5	syl3anc	$$⊢\phi \to \eta$$