Performing variable elimination by substitution in a chart-record.
The substitutions eliminates the listed affine variables of the chart,
reducing drastically the time needed for Gröbner basis computations on
- a chart record,
- the list of pairs [k, eq], where k is
an index to the S member of the chart, and eq is
the substitution equation for it.
- the chart-record with the given substitutions performed.