?. L. De-biagi and &. R. Puccinelli, Grey crossroads' in cultural heritage preservation and resource management, GL18 Eighteenth International Conference on Grey Literature, 2016.

?. M. Lourenço and &. L. Wilson, Scientific heritage: Reflections on its nature and new approaches to preservation, study and access, Studies in History and Philosophy of Science Part A, vol.44, issue.4, pp.744-753, 2013.

?. M. Ramos-lum and &. S. Vogel, Entering Grey Waters: Challenges and Solutions of Providing Access to Non-traditional literature in an Aquarium's library', GL7 Seventh International Conference on Grey Literature, 2005.

?. J. Schöpfel, Vers une nouvelle définition de la littérature grise'. Cahiers de la Documentation, Bladen voor Dokumentatie, vol.66, issue.3, pp.14-24, 2012.

?. J. Schöpfel-&-d and . Farace, Grey literature', Encyclopedia of library and information sciences, 2017.

?. J. Schöpfel, What about ODTs? Are they grey?, 11th Conference on Grey Literature and Repositories, National Library of Technology (NTK), 2018.