6 lines
274 B
Text
6 lines
274 B
Text
namespace List
|
||
-- Should not panic
|
||
#guard_msgs (drop error) in
|
||
theorem countP_filterMap' {p : β → Bool} {f : α → Option β} {l : List α} :
|
||
countP p (filterMap f l) = countP (fun a => ((f a).map p).getD false) l := by
|
||
induction l with grind [=_ Option.getD_map]
|