+"`elemIndex el lst` returns the index of the first element in the given list `lst` which is equal (by ==) to the query element, or Nothing if there is no such element."
+elemIndex :: a -> [a] -> Maybe Integer
+elemIndex el l = loop 0
+ where
+ len = length l
+ loop i | i < len = if el == l!i
+ then Just i
+ else loop (i+1)
+ | otherwise = Nothing
+
"""
Computes a list that contains only elements that belongs to both input lists.
"""
"""
Computes a list that contains only elements that belongs to both input lists.
"""
@@ -2023,6+2088,7 @@ Transposes the rows and columns of its argument. For example,