text: Title: Increase number of bibliographical entries in glossary
  Body: I think it would be good if we included a few more citations in the glossary.  In particular, it would be good to have a few references to trace the history of persistent homology.  A few such are listed in the first page of https://www.maths.ed.ac.uk/~v1ranick/papers/edelhare.pdf, and an even earlier precursor is the 1994 paper by Barannikov [The Framed Morse complex and its invariants](https://hal.archives-ouvertes.fr/hal-01745109/document).