English
If p and q are decidable propositions and p ↔ q, then decide(p) = decide(q).
Русский
Если p и q — разрешимые пропозиции и p ⇔ q, тогда decide(p) = decide(q).
LaTeX
$$$$ \forall p\, q\, [\operatorname{Decidable}(p)]\,[\operatorname{Decidable}(q)]\,(p \leftrightarrow q)\Rightarrow \operatorname{decide}(p) = \operatorname{decide}(q) $$$$
Lean4
theorem decide_congr {p q : Prop} [Decidable p] [Decidable q] (h : p ↔ q) : decide p = decide q :=
decide_eq_decide.mpr h