Person. Gordon Plotkin [plotkin]

Professor
University of Edinburgh
https://homepages.inf.ed.ac.uk/gdp/

Backlinks

LFCS 40 [loc-005H]

September 9, 2026
Liam O'Connor

We had a celebration of 40 years since the foundation of the Laboratory for Foundations of Computer Science (LFCS) by Robin Milner, Rod Burstall and Gordon Plotkin today. This was the institute that I was (and in some sense, remain) part of at the University of Edinburgh. I don't have much time for navel-gazing, and sadly most of the technical talks were either well outside my area, a demonstration of how brain-poisoned by LLMs my former Edinburgh colleagues have become, or both. I didn't really get much out of the day.

I am still glad to be here in Edinburgh for this week, though. It's great to catch up with some old friends.

Happy Birthday, Gordon Plotkin [loc-005G]

September 8, 2026
Liam O'Connor

We had a celebration of Gordon Plotkin's eightieth birthday today, featuring many interesting talks. It's hard not to run into Gordon's work if you do anything involving semantics or concurrency or programming languages. My favourite talk of the day was probably my friend Ningning Xie's talk, but I also enjoyed Rob van Glabbeek's talk on his Justness work.

My only major Gordon anecdote is that he was on my interview panel when I interviewed for the job at the University of Edinburgh, and I was astounded to realise that not only was he still alive, but also he somehow didn't appear much older than any of the famous pictures of him.

So, congratulations and happy birthday to the timeless Gordon Plotkin, a huge contributor to our field and an intellectual hero to many of us.

The Plotkin powerdomain [dt-0067]

Liam O'Connor

As before, let $X, Y \in \mathcal {P}_f^\ast (\mathsf {K}(A))$ be finite, non-empty sets of compact elements of a Scott domain $A$ . The Plotkin powerdomain construction is based on the following preorder, simply combining the orderings from the Hoare and Smyth constructions: $X \preceq _P Y\quad \text {iff}\quad X \preceq _H Y \land X \preceq _S Y$ This ordering is also called the Egli-Milner ordering. On a flat domain, it simplifies to: $A\sqsubseteq B\quad \text {iff}\quad A = B \lor (\bot \in A \land (A \setminus \{\bot \})\subseteq B)$ Note that this is antisymmetric in the case of a flat domain, and the lub of a chain of sets can be found by taking the union of all elements of the chain if all elements contain $\bot$ If not, then the element without $\bot$ will be the least upper bound.

The failures of antisymmetry can only be observed in domains of height higher than one. Consider a set $\{x,y\}$ containing two elements. According to the induced equivalence from this preorder $\approx _P$ , this set would be considered equal to the set that contains those two elements plus any elements that lie between them on the information ordering: $\{x,y\} \approx _P \{ z \mid x \sqsubseteq z \sqsubseteq y \}$ The Plotkin powerdomain is sometimes called the convex powerdomain, due to the similarity of this to the geometric definition of convexity. Thus, we use the ideal completion trick (as with the Hoare and Smyth constructions) here to arrive at a definition of powerdomain that distinguishes between all three programs outlined in Remark [dt-0063].

Aside.

Liam O'Connor

There is a beautiful algebraic characterisation of Plotkin powerdomains in Matthew Hennessy Gordon Plotkin's paper, Full abstraction for a simple parallel programming language.

Institution. University of Edinburgh [uoe]

Scotland, United Kingdom
https://ed.ac.uk

Contributions

Reference. Full abstraction for a simple parallel programming language [hennessy-plotkin-1979]

September 7, 1979
Matthew Hennessy, Gordon Plotkin
MFCS '79: Mathematical Foundations of Computer Science 1979
10.1007/3-540-09526-8_8