Coordinates in two variables over a $\mathbb {Q}$-algebra
Coordinates in two variables over a $\mathbb {Q}$-algebra
This paper studies coordinates in two variables over a $\mathbb {Q}$-algebra. It gives several ways to characterize such coordinates. Also, various results about coordinates in two variables that were previously only known for fields, are extended to arbitrary $\mathbb {Q}$-algebras.