In his technical report (MR 34) of October 1961, Dijkstra explained why he viewed a good programming language to be one of a small number of very general concepts. To clarify, he used an analogy between mathematics and programming, an analogy which in later years would be scrutinized in several ways by his contemporaries. (See e.g. MacKenzie's 2004 book Mechanizing Proof: Computing, Risk, and Trust.)
In the late summer of 1981, Dijkstra gave several talks in Scotland and Newcastle. Here is an overview of his trip:
+ The Marine Hotel in North Berwick. The host was Mr. Hannah of Burroughs. The audience consisted of 10 men from various Burroughs plants in Europe. Dijkstra lectured for five successive days, between 6 and 7 hours per day. The "standard surprise" from the audience was that the universal quantification over the empty set yields true.
The theme of the International Summer School in Marktoberdorf was "Theoretical Foundations of Programming Methodology". The general pattern of the day was: two lectures — a break — two lectures — lunch — two lectures — break — discussion.
In his trip report, Dijkstra listed several speakers from that summer school:
Roughly 80 participants from 15 countries participated in the 1971 summer school in Marktoberdorf. According to Dijkstra, some participants were very theoretically inclined, others more practically minded. Viewed from the present day, the following list of speakers at that summer school is impressive. Dijkstra attributed a theme to each speaker, with the exception of Perlis and Dahl:
The T.H.E. multiprogramming system — as designed and implemented by Dijkstra, Bron, Habermann, Hendriks, Ligtmans, and Voorhoeve — was studied by Mike McKeag during his visit to Eindhoven some time during the first half of 1971. Subsequently, McKeag went back to his university in Belfast (in Hoare's research group) where he wrote a report of the T.H.E. system. That report was sent to Dijkstra on 22 July 1971 with a cover letter stating:
About 65 participants, including Dijkstra, attended the "Advanced Course on Functional Programming and its Applications" at the University upon Tyne (20-31 July 1981). The following points are of general interest because they seem to have recurred throughout Dijkstra's career:
Dijkstra visited the USA several times before moving to Texas in 1984. In the summer of 1971, he went on a trip to the USA and Canada. It wasn't his first trip to North America, but it was the first time his wife Ria accompanied him. The corresponding trip report was written by Dijkstra on June 23rd, 1971 in EWD312.
Dijkstra's Structured Programming abided by a top-down presentation of his programs. In the Spring of 1981, Van Gasteren and Dijkstra recommended a similar presentation style for mathematical arguments. For instance, they advocated using lemmata before giving their proofs:
Though unusual, this seems entirely correct. The statement of a lemma is a logical firewall between its usage and its proof; the use of a lemma is independent of how the lemma can be proved and, during study of its use, knowledge of its proof is therefore an unnecessary burden. [AvG5/EWD788 - 5]