In constructing polynomial rings, documentation says that diamond brackets are used "to make the variable ready for use after you define the ring", but the variables are entered explicitly: R.<x,y> .
E.g. if I have xs = [x_1,x_2,x_3], I want to construct a polynomial ring and subsequently manipulate x_1 + x_2, etc., within that ring instead of "symbolic ring". I'd like to do something like R.<xs> but that doesn't seem to work.