grades() of the zero freealg object

[RobinHankin]

Knuth [TAOCP, volume 2, p436] defines the degree() of a freealgebra object [I call this the grade()] to be $-\infty$ but:

> grades(rfalg()*0)
[1] 0
> 

[RobinHankin]

Actually he defines degree as follows

degree <- function(x){max(grades(x))}