A Festschrift volume is always a bit different than standard collections of papers: while they usually still possess a definite set of themes, as the current one does, there is also a certain freedom to explore ideas in a different way. This is due, in part, to the fact that such papers have less constraints (on length, scientific novelty, and so on); authors can take advantage of this to write a “gem” of a paper that simultaneously explains some ideas and pays tribute to the honorees, in this case, Hanne Riis Nielson and Flemming Nielson. Both have worked on a variety of topics, largely centered on program analysis.

The collection at hand contains a fairly varied set of contributions, quite well anchored around the themes of the Nielsons’ work. Some are real gems that really take advantage of the freedom afforded by a Festschrift. Others are more typical research papers. The overall quality is excellent. The variety of topics touched is quite broad, but this is because the techniques of program analysis can indeed be applied to a broad set of situations.

What is a little surprising are the four papers that do not cite any of the Nielsons’ work; granted, one does mention them in-line, while another is from a close collaborator, but this still seems incongruous. Other papers only mention one or two of their (wonderful!) textbooks [1-3]. The contributions that stand out are actually the ones that tend to cite some of the Nielsons’ research papers.

Nevertheless, anyone who enjoys program analysis will find some papers here to appreciate. While I do not personally know the Nielsons (but I have benefited from their work), I certainly hope they found that this was a fitting set of essays.