diff --git a/content/24.sup.note.4.md b/content/24.sup.note.4.md
index ffcca93..ed87f40 100644
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+++ b/content/24.sup.note.4.md
@@ -21,7 +21,7 @@ Inside our framework, these languages can be freely and transparently exchanged,
 However, most tie themselves tightly to a particular standard format or modelling language ecosystem, thereby inheriting many of the limitations described above.
 The Knowledge Graph Hub provides a data loader pipeline, KGX allows conversion of KGs between different technical formats, and RTX-KG2 builds a fixed semantically standardised KG; all three adhere to the Biolink model [@doi:10.1101/2020.08.17.254839;@doi:10.1186/s12859-022-04932-3].
 Bio2BEL is an extensive framework to transform primary databases into BEL [@doi:10.1101/631812].
-PheKnowLator is the only tool that is conceptually similar to BioCypher in that it allows the creation of knowledge graphs under different data models 14.
+PheKnowLator is the only tool that is conceptually similar to BioCypher in that it allows the creation of knowledge graphs under different data models [@doi:10.1101/2020.04.30.071407].
 However, it appears to be aimed at knowledge representation experts, requiring considerable bioinformatics and ontology expertise.
 While being fully customisable, it does not feature flexible recombination of modular components.