Based on the subject provided, the "proper piece" you are looking for is most likely a bibliographic citation or a descriptive summary of the educational resource in question. "Matematičke formule" by Dragoslav Herceg is a well-known handbook for students in Serbia and the region.
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Educational Repositories: Recent uploads to university portals or student forums intended to provide free study materials during exam seasons. About the Author Based on the subject provided, the "proper piece"