English
Scanl on a cons lists satisfies a simple formula: scanl f b (a :: l) = [b] ++ scanl f (f b a) l.
Русский
Scanl на конc-список удовлетворяет формуле: scanl f b (a :: l) = [b] ++ scanl f (f b a) l.
LaTeX
$$$$\operatorname{scanl} f b (a\;::\;l) = [b] \;++\; \operatorname{scanl} f (f\;b\;a) l.$$$$
Lean4
@[simp]
theorem scanl_cons : scanl f b (a :: l) = [b] ++ scanl f (f b a) l := by simp only [scanl, singleton_append]