The aim of the article is to indicate the biographical sources used by the author and to introduce some still unpublished biographical data of Josef Tvrdý. They are first of all the materials deposited in the Archive of the Masaryk University in Brno (Czech Republic) and of Comenius University in Bratislava (Slovak Republic). These approve the validity of the biographical data published in this article. Among the new materials the most interesting are: the certificate affirming Tvrdý's graduation from the high school, the university records, the administrative and personal letters, the report of the habilitation commission and the various personal and autobiographical notes (mainly the reconstruction of his thesis defense and habilitation agenda) and the events related to his enforced leaving the Comenius University, his arresting and his death in the concentration camp Mauthausen.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.