-- | difference of Signatures
sigDiff :: Sign -> Sign -> Sign
sigDiff sig1 sig2 = sig1 {items = Map.difference (items sig1) $ items sig2}
sigDiff :: Sign -> Sign -> Sign
sigDiff sig1 sig2 = sig1 {items = Map.difference (items sig1) $ items sig2}
sigDiff sig1 sig2 = sig1 {items = Map.difference (items sig1) $ items sig2}