This is wrong, I think.  Imagine that you have a Mat defined between a non mixed and a mixed space. then maps[0] is not mixed, but maps[1] is.

I think you probably want (for both cases)

````python
for map in maps:
    for m in map:
        if m.iterset.layers is not None and m.iterset.layers > 1:
            _args.append(m.offset)
````