NSSet <NSString> SelectableLayersFromSources(string [] layersId)
        {
            if (layersId == null)
            {
                return(null);
            }

            NSMutableSet <NSString> output = new NSMutableSet <NSString>();

            foreach (string layerId in layersId)
            {
                var acceptedId = layerId.Replace("_", "-");
                output.Add((NSString)acceptedId);
                output.Add((NSString)(acceptedId + " (1)"));
            }
            return(output.Copy() as NSSet <NSString>);
        }