### The Catsters’ Latest Hit: “Adjunctions”

#### Posted by John Baez

Who knew category theory could be so popular? The Catster’s videos on Monads have taken Youtube by storm! As of this moment, the first episode has garnered 3758 viewings, prompting one disgruntled teenager to suggest that the Catsters are *cheating* in the battle for high ratings:

> Its really funny that your most of

> your subscribers have no videos, are

> subscribed to only you, and have only your

> videos as favorites. Do I sense a youtube

> cheater?

Of course, we Catsters fans know it ain’t so — they’re just satisfying a hitherto unnoticed craving for math lectures on YouTube!

And the Catsters are on a roll. Now they’ve tackled adjoint functors, also known as ‘adjunctions’:

- The Catsters, 7 lectures on Adjunctions.

Their edgy, low-budget production makes for gripping cinema. This is the real stuff.

For more on monads and adjunctions, try old episodes of *The Tale of n-Categories* (which will soon be made into a movie starring Emma Watson and Orlando Bloom). In week83 I described adjunctions in an arbitrary 2-category; in week89 I did the same for monads, and in week92 I described how adjunctions give monads.

## Re: The Catsters’ Latest Hit: “Adjunctions”

Yes, there’s an electrifying moment which occurs at 9:27 in Adjunctions 2. :-)

Eugenia is really good at making these nice categorical points in under 10 minutes (the usual time limit on Youtube). Good sense of dramatic timing too; perhaps her experience as a musical performer has helped. (Although I didn’t recognize the tune she hums to the accompaniment of the pasting diagram equations for adjunctions!)

Keep ‘em coming, Catsters!