static L deleteOldConcepts(Concepts cc default db_mainConcepts(),
Class conceptClass, double minAgeInSeconds) {
new L deleted;
for (A c : cloneList(list(cc, conceptClass)))
if (max(c._modified, c.created) < now()-toMS(minAgeInSeconds)) {
print("Deleting concept " + c);
deleted.add(c);
cdelete(c);
}
ret deleted;
}