English
If s1.entries is a permutation of s2.entries, then (replace a b s1).entries is a permutation of (replace a b s2).entries.
Русский
Если s1.entries пера перестановка s2.entries, то (replace a b s1).entries перестановка (replace a b s2).entries.
LaTeX
$$s_1.entries \sim s_2.entries \Rightarrow (replace(a,b,s_1)).entries \sim (replace(a,b,s_2)).entries$$
Lean4
theorem perm_replace {a : α} {b : β a} {s₁ s₂ : AList β} :
s₁.entries ~ s₂.entries → (replace a b s₁).entries ~ (replace a b s₂).entries :=
Perm.kreplace s₁.nodupKeys