mulSigSubKey :: [XPubKey]       -- ^ List of extended parent public keys
             -> Word32          -- ^ Child key derivation index
             -> Maybe [XPubKey] -- ^ List of extended child public keys
mulSigSubKey pubs i = mapM (flip pubSubKey i) pubs
mulSigSubKey :: [XPubKey]       -- ^ List of extended parent public keys
             -> Word32          -- ^ Child key derivation index
             -> Maybe [XPubKey]
mulSigSubKey pubs i = mapM (flip pubSubKey i) pubs
mulSigSubKey pubs i = mapM (flip pubSubKey i) pubs