\item a phylogenetic tree which may contain multichotomies;
\item a formula which specifies the predictors of the model described
- above: this is given as a standard R formula and has no response (no
+ above: this is given as a standard \R formula and has no response (no
left-hand side term), for instance: \code{~ x + y}, it can include
interactions (\code{~ x + a * b}) (see \code{\link[stats]{formula}}
for details);