isSubsequenceOf a@(x:a') (y:b) | x == y    = isSubsequenceOf a' b
                               | otherwise = isSubsequenceOf a b
isSubsequenceOf a@(x:a') (y:b) | x == y    = isSubsequenceOf a' b
                               | otherwise = isSubsequenceOf a b
isSubsequenceOf a@(x:a') (y:b) | x == y    = isSubsequenceOf a' b
                               | otherwise = isSubsequenceOf a b