Theorem stoic2b

Stoic logic Thema 2 version b. See stoic2a. Version b is with the phrase "or both". We already have this rule as mpd3an3, so here we prove the equivalence and discourage its use. (New usage is discouraged.) (Contributed by David A. Wheeler, 17-Feb-2019.)

Hypotheses
stoic2b.1
\( \vdash \varphi \wedge \psi \rightarrow \chi \)
stoic2b.2
\( \vdash \varphi \wedge \psi \wedge \chi \rightarrow \theta \)
Conclusion
\( \vdash \varphi \wedge \psi \rightarrow \theta \)
Proof
l0
stoic2b.1
\( \vdash \varphi \wedge \psi \rightarrow \chi \)
stoic2b.2
\( \vdash \varphi \wedge \psi \wedge \chi \rightarrow \theta \)
mpd3an3 l0 _