Lecture 3 and an addendum for subgroups of free groups

This is now a reworking of Lecture 3. It describes how to generate a subgroup H of a group G with a given set of generators when one is also given a transversal of H in G. This leads one naturally to a proof of Schreier's theorem which asserts that subgroups of free groups are free. This proof was not given in class but is here described in detail. Some exercises will be provided in due course which show how this proof actually works in some concrete cases.

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