Things that are hard:

Paying attention in algebraic number theory while working on (and solving!) the following problem from a friend: find two nonisomorphic graphs with the same multisets of vertex degrees, the same multisets of lengths of maximal (that is, unextendable, not maximum-length) paths, and the same multiset of lengths of cycles. (Fortunately, the second half of class was review of something I’d understood the first time, so it didn’t take my full attention.)

Figuring out enough of a weeklong, not-quite-finished test I didn’t write to edit and contribute a bit to it, on short notice.

Preparing to talk about, in class, Putnam problem 6s about calculating nasty integrals. [Yay for getting requests from students for specific problems, which means they’ve thought more about them than average, but did they have to request that problem?.]

Getting, using only Hungarian, train tickets and hostel accommodations on short notice [here, the short notice my fault] [the first hostel I tried, yesterday, was booked].

Today was a productive day.