I'm reading some paper where they haven't really defined their notation very well (or I've missed something). You can see the image below.
What does the square bracket and star mean precisely? The context is that a space (with a group acting on it) is partition into $[G_1, G_2]$. Is it some representation or some lift, something to do with cosets or something else?
Paper link is here: https://arxiv.org/abs/2002.11259