Parenthetic remarks

Ross Street – 18 June 1997

I seem to be writing a gentle introduction to operads! It and the talk start by looking at the set-theoretical version of Stasheff's operad k that arises from parenthesising and heads towards Batanin's operad h (which is like k but takes units into account). This leads to the melding of various subjects: Lawvere theories, species, combinatorical generating functions, virtual sets, monoidal categories, string diagrams, and Kelly clubs. The criterion of Eilenberg for when a Polish expression should be meaningful is used.