ICode9

Functor 怎么会事呢 Functor 2 axioms \(F(id_A) = id_{F(A)}\) \(F(f \circ g) = F(f) \circ F(g)\) 这两个公理能证明 \[F(f(A)) = F(f)(F(A)) \]吗？ 还真能 变一下形式 即证: \[(F\circ f) (A) = (F(f) \circ F) (A) \]只需 \[\begin{aligned} F \circ f =& F(f) \circ F