diff --git a/syndicate/doc/what-is-an-actor.md b/syndicate/doc/what-is-an-actor.md
index 08b0e6e..039dbc7 100644
--- a/syndicate/doc/what-is-an-actor.md
+++ b/syndicate/doc/what-is-an-actor.md
@@ -1,8 +1,8 @@
# What is an Actor?
-A [Syndicated Actor][Actor] is a collection of stateful
-[Entities][Entity], organised in a tree of [Facets][Facet], with each
-facet representing a
+A [Syndicated Actor][Actor] ([Garnock-Jones 2017](#GarnockJones2017))
+is a collection of stateful [Entities][Entity], organised in a tree of
+[Facets][Facet], with each facet representing a
[(sub)conversation](https://syndicate-lang.org/about/#conversational-concurrency-1)
that the Actor is engaged in. Each entity belongs to exactly one
facet; each facet has exactly one parent and zero or more children;
@@ -22,8 +22,17 @@ similar to that offered by the E programming language
**References.**
- De Koster, Joeri, Tom Van Cutsem, and Wolfgang De Meuter. “43 Years of Actors: A Taxonomy of Actor Models
- and Their Key Properties.” In Proc. AGERE, 31–40. Amsterdam,
- The Netherlands, 2016.
- [DOI](https://doi.org/10.1145/3001886.3001890).
+ name="DeKoster2016"
+ href="http://soft.vub.ac.be/Publications/2016/vub-soft-tr-16-11.pdf">“43
+ Years of Actors: A Taxonomy of Actor Models and Their Key
+ Properties.” In Proc. AGERE, 31–40. Amsterdam, The
+ Netherlands, 2016. [DOI](https://doi.org/10.1145/3001886.3001890).
[PDF](http://soft.vub.ac.be/Publications/2016/vub-soft-tr-16-11.pdf).
+
+ - Garnock-Jones, Tony. “Conversational
+ Concurrency.” PhD, Northeastern University, 2017.
+ [Permalink](http://hdl.handle.net/2047/D20261862).
+ [PDF@Northeastern](https://repository.library.northeastern.edu/files/neu:cj82qs441/fulltext.pdf).
+ [PDF@syndicate-lang.org](https://syndicate-lang.org/papers/conversational-concurrency-201712310922.pdf).
+ [HTML](https://syndicate-lang.org/tonyg-dissertation/html/).