How do I combine selection masks?

I have a layer with two local selections. I need a third local selection, consisting on the addition of the two:

1st row: Base
2nd row: First selection
3rd row: Second selection
4th row: Intended final mask

But Krita won’t let me merge or apply blending modes to local selections.

Help?

Never mind, figured it out:

  1. Duplicate both local selections
  2. Convert them to paint layers (right click on Layers docker > Convert > to Paint Layer)
  3. Blend layers, then merge them
  4. Convert to local selection (right click on Layers docker > Convert > to Selection Mask)

It’s rather clumsy. Follow-up question: Is there a way to do this faster? I need to juggle a bit of a selection mask jigsaw puzzle.

For your step 3. above, you could use the Addition layer blending mode and then do ‘New Layer From Visible’ then convert the new layer to a local selection. (Or is that what you already did and meant by ‘mathematical operation’?)
I can’t figure out a rapid way of doing it.

Yes, that’s what I meant. I just edited “perform mathematical operation” into “blend layers,” hopefully to make it more clear.