J. Rakosnik, P. Stanchev, G. Simeonov, and R. Pavlov, “Bulgarian Digital Mathematical Library BulDML and Czech Digital Mathematical Library DML-CZ as parts of the European Digital Mathematics Library EuDML”, DiPP, vol. 2, pp. 60–68, Sep. 2012, doi: 10.55630/dipp.2012.2.27.