Can someone point me to a reference where the notion of "Lie crossed module" appeared for the first time?


I see many papers "recall" the definition of the Lie crossed module but, I do not see any mention of a "first-time" reference.


The definition of Lie crossed module I am referring to is mentioned as Definition 1.3 in


* João Faria Martins and Roger Picken, *On Two-Dimensional Holonomy*, Trans. Amer. Math. Soc. **362** (2010) pp. 5657-5695, doi:[10.1090/S0002-9947-2010-04857-3](https://doi.org/10.1090/S0002-9947-2010-04857-3), arXiv:[0710.4310](https://arxiv.org/abs/0710.4310).



First time appearance of Lie crossed module (crossed module of Lie groups) in literature
Crossed modules of Lie algebras are defined by Kassel and Loday in Definition A.1 of [Extensions centrales d’algèbres de Lie](https://doi.org/10.5802/aif.896) (published 1982).


Crossed modules of Lie groups are defined by Mackenzie in Definition 1.5 of [Classification of principal bundles and lie groupoids with prescribed gauge group bundle](https://doi.org/10.1016/0022-4049(89)90157-6).
Definition 3.3 there defines crossed modules of Lie groupoids (published 1989).


Crossed modules of local Lie groupoids are defined by Brown and İçen in Definition 4.1 of [Towards a 2-dimensional notion of holonomy](http://doi.org/10.1016/s0001-8708(02)00074-9) (published 2003).


