Theorem syldc

Syllogism deduction. Commuted form of syld. (Contributed by BJ, 25-Oct-2021.)

Hypotheses
syld.1
\( \vdash \varphi \rightarrow \psi \rightarrow \chi \)
syld.2
\( \vdash \varphi \rightarrow \chi \rightarrow \theta \)
Conclusion
\( \vdash \psi \rightarrow \varphi \rightarrow \theta \)
Proof
l0
syld.1
\( \vdash \varphi \rightarrow \psi \rightarrow \chi \)
syld.2
\( \vdash \varphi \rightarrow \chi \rightarrow \theta \)
syld l0 _
com12 _