Distribute substitution over implication. Closed form of sbimi.
Specialization of implication. (Contributed by NM, 5-Aug-1993.) (Proof
shortened by Andrew Salmon, 25-May-2011.) Revise [df-sb]. (Revised by
BJ, 22-Dec-2020.) (Proof shortened by Steven Nguyen, 24-Jul-2023.)
\( \vdash \forall x \, (\varphi \rightarrow \psi) \rightarrow [ t' / x ] \, \varphi \rightarrow [ t' / x ] \, \psi \)
\( \vdash \forall x \, (\varphi \rightarrow \psi) \rightarrow [ t' / x ] \, (\varphi \rightarrow \psi) \)
\( \vdash [ t' / x ] \, (\varphi \rightarrow \psi) \rightarrow [ t' / x ] \, \varphi \rightarrow [ t' / x ] \, \psi \)