cache -- a key under which to store cache tables

Caches the result of the function gradedBettiChampion, which uses double recursion.

Once gradedBettiChampion(ZZ) finishes, the table is cleared.

If you want to keep the results, use the method gradedBettiChampion(ZZ,ZZ) instead. Note that gradedBettiChampion(c,c) = gradedBettiChampion(c).

i1 : time(gradedBettiChampion(20,20));
     -- used 6.734 seconds

i2 : time(gradedBettiChampion(20));
     -- used 0. seconds

i3 : time(gradedBettiChampion(20));
     -- used 6.782 seconds