Aspects of quasi-randomness: IX Cohomological aspects of hypergraphs.

This is the ninth in a series of memoranda dealing with certain aspects of randomness occurring in the mathematical sciences. The use of "random" structures and "random" algorithms plays an essential role in a variety of disciplines, which includes mathematics, theoretical computer science and communication theory, to name a few. Indeed, Shannon's fundamental results on the existence of good error-correcting codes, and Erdos' classical proof of the existence of graphs on n vertices which have maximum cliques and independent sets of size 2 log n are some of the earliest examples of the power of employing random structures. One of the most fruitful applications of these ideas is the so-called "probabilistic method".