As an experiment, I just did a search for “Equivalence Relations” (with or without the s) on iTunes. Very little turns up in the search results. The only Collection shown is my G11FPM, and the only iTunes U Episode shown is one of my lectures. That seems surprisingly little given how many institutions are making materials available out there.
Compare this with a search on YouTube:
gives over 3000 results, and my lecture on this only just makes it into the current top 20.
Is it just this topic where few of the iTunes U Universities are contributing? Or is it a more general pure mathematics shortage on iTunes U? Or is it a metadata problem, where not enough content detail is included in the iTunes descriptions?