private GdlVariable renameVariable(GdlVariable variable, Map<GdlVariable, GdlVariable> renamings)
{
if (!renamings.containsKey(variable))
{
GdlVariable newName = GdlPool.getVariable("?R" + (nextName++));
renamings.put(variable, newName);
}
return renamings.get(variable);
}