f <$ a ≡ mapped .~ f $ a
>>> (a,b,c,d) & _4 .~ e (a,b,c,e)
>>> (42,"world") & _1 .~ "hello" ("hello","world")
>>> (a,b) & both .~ c (c,c)
(.~) :: Setter s t a b -> b -> s -> t (.~) :: Iso s t a b -> b -> s -> t (.~) :: Lens s t a b -> b -> s -> t (.~) :: Traversal s t a b -> b -> s -> t