1. This function modifies the internal representation of a set in order to improve the efficiency of function getelsetval. After this function has been called, the set must not be modified until unmapset is used.

2. This function is effective only on dynamic general sets, it is however safe to use it on other type of sets (range and/or constant sets).

3. If the function is used several times on a given set, unmapset has to be called the same number of times to restore the set in its initial state.

4. If several sets are mapped, it is preferable to call unmapset in reverse order to minimise memory fragmentation ( i.e. mapset(ctx,s1); mapset(ctx,s2) ... unmapset(ctx,s2); unmapset(ctx,s1)).