Multiple brushes in a layer

[gareth]

I am hoping someone can point me to the best way to work with an additive and a subtractive brush in the same layer
---preferably, to be able to move backward and forward between them.
This may be something that will be improved with the other fixes to the layer panel ( eg, the expanding of layers other than the one you select)

I create the first brush (additive) and work with it.
I cannot then just click on the brush tool to create the second brush -- one just ends up in the same brush.
I need to do something unrelated to layers and brushes that makes ASP forget the brush -- my best effort so far is to apply a preset and then unset it (as I mentioned in Bibble some time ago)
I can then create a new (subtractive) brush and work with that.
I then don't seem to be able to just click on the first brush to continue working with that one.

In case you ask why the subtractive brush is important ...
The normal/eraser buttons at the bottom are very useful when working within one brush to refine it ... but the eraser brush does not act as a subtractive brush on an existing polygon.