I think GP was making a math joke; "a group is a non-empty set [...] in such a way that [...] every element has an inverse". [0] [0] https://en.m.wikipedia.org

I think GP was making a math joke; "a group is a non-empty set [...] in such a way that [...] every element has an inverse". [0] [0] https://en.m.wikipedia.org/wiki/Group_(mathematics) https://en.m.wikipedia.org/wiki/Group_(mathematics)