You may have learned this in 5th or 6th grade, but I certainly didn't. The point is that any working mathematician is comfortable manipulating sets in algebrai

You may have learned this in 5th or 6th grade, but I certainly didn't. The point is that any working mathematician is comfortable manipulating sets in algebraic expressions and that's not something you expect from your average high schooler. I could have added that mathematicians need to know at least about different cardinalities, but I guess strictly speaking you could be working in discrete maths and not care about any of this.