Personalization of learning costs

[laowantong]

Currently, the learning costs are calculated with a simple mathematical formula. This approach is obviously very basic. One could imagine letting the teacher provide the learning cost associated with the introduction of this or that concept, such as the number of minutes he or she spent on it in the previous year. This doesn't seem difficult to set up: it would be enough to read a TSV file associating taxa and learning costs, falling back on the mathematical formula.