Two Stations' Play Logs

Two radio stations each keep a log of the day's plays: a list of song titles, one entry per play, in the order they aired. The music director wants the songs that aired exactly once — not zero times, not twice — on each of the two stations.

Task: write played_once_on_both(log_a, log_b) that returns those titles as a list in alphabetical order (the order sorted gives).

• Titles must match exactly, capital letters included: "Kites" and "kites" are different songs.
• A song played twice on one station doesn't count, however many times the other station played it.
• Either log may be empty. If no song qualifies, return [].

"Neon Tide" and "Glass Hour" aired on both stations as well, but each one was played twice on one of them.