Theorem stoic2a

Description: Stoic logic Thema 2 version a. Statement T2 of Bobzien p. 117 shows a reconstructed version of Stoic logic thema 2 as follows: "When from two assertibles a third follows, and from the third and one (or both) of the two another follows, then this other follows from the first two." Bobzien uses constructs such as ph , ps |- ch ; in Metamath we will represent that construct as ph /\ ps -> ch . This version a is without the phrase "or both"; see stoic2b for the version with the phrase "or both". We already have this rule as syldan , so here we show the equivalence and discourage its use. (New usage is discouraged.) (Contributed by David A. Wheeler, 17-Feb-2019)

	Ref	Expression
Hypotheses	stoic2a.1	|- ( ( ph /\ ps ) -> ch )
	stoic2a.2	|- ( ( ph /\ ch ) -> th )
Assertion	stoic2a	|- ( ( ph /\ ps ) -> th )

Proof

Step	Hyp	Ref	Expression
1		stoic2a.1	|- ( ( ph /\ ps ) -> ch )
2		stoic2a.2	|- ( ( ph /\ ch ) -> th )
3	1 2	syldan	|- ( ( ph /\ ps ) -> th )