The model fitting function loglm fits log-linear models to
frequency data using iterative proportional scaling. To specify
the model the user must nominate the margins in the data that
remain fixed under the log-linear model. It is convenient to
allow the user to use dimension numbers, 1, 2, 3, ... for the
first, second, third, ..., margins in a similar way to variable
names. As the model formula has to be parsed by terms, which
treats 1 in a special way and requires parseable variable names,
these formulae have to be modified by giving genuine names for
these margin, or dimension numbers. denumerate replaces these
numbers with names of a special form, namely n is replaced by
.vn. This allows terms to parse the formula in the usual way.