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.