A direct proof of Tychonoff's theorem

Abstract

Proofs of Tychonoff's theorem often seem to require a bit of magic. Machinery such as ultrafilters, nets or maximal families with the finite intersection property are employed to give proofs that can be very neat, but not the kind of thing that one would naturally think of when presented with the problem (given a background in standard open set topology). Here we present a direct and pretty simple proof of Tychonoff's theorem, straight from the open cover definition of compactness.