Huh, it appears a lot less frequent than I thought. I had misremembered some \mathrm{R}'s as \mathbf{R}'s. That said, I still feel that I've seen every \mathbf

Huh, it appears a lot less frequent than I thought. I had misremembered some \mathrm{R}'s as \mathbf{R}'s. That said, I still feel that I've seen every \mathbf letter used for something other than a standard number set somewhere. But probably not in the mainstream.