95 lot of memory is needed onnfa 3dot

[Numero7]

Cache system is dropped.

Two new heuristics for iterating through candidate ideals when computing the presafe image by a letter:

• when finding a good ideal, avoid iterating in smaller ideals.
• when iterating on a coordinate 0 first, then omega, then finite coordinates by descending order. If it is losing for 0, there is no need to push further the exploration with other coordinates larger or equal.