The true expert realizes what question is being asked, and grabs a calendar. Two people, equally knowledgeable and given the same problem, will not necessarily

The true expert realizes what question is being asked, and grabs a calendar. Two people, equally knowledgeable and given the same problem, will not necessarily come up with the same solution. Leap years are not a mathematical fact; they are an engineering solution to a mathematical challenge. An expert looking at orbits is unlikely to decide that we must specifically add an extra day to February; you only know that we use this solution by deriving it from calendars.