PRINSIPI DUGONIYaT, prinsipest, ki dar baze qismathoi matematika istifoda meshavad va manii zerin dorad: ba har yak tasdiqoti durusti in qismati matematika guftori dugonae muvofiq meoyad, ki az tasdiqoti avvala dar surati bo mafhumhoi digar — ba istiloh dugona —ivaz kardani mafhumhoi tarkibii vay hosil meshavad.
1) Prinsipi dugoniyat dar geometriyai proektivi. In jo Prinsipi dugoniyat dar hamvori muqarrar karda meshavad. Mafhumhoi dugona inhoand: «nuqta» va «khati rost», «nuqta dar khati rost voqe ast» va «khati rost az nuqta meguzarad». Baroi dar yak tasdiqot guftori dugonaero yoftan mumkin ast, ki tavassuti khudi hamin aksiomaho muayyan karda meshavad.
2) Prinsipi dugoniyat dar nazariyai a b stran t i i majmuho. Biguzor majmui M doda shuda boshad. Sistemai hamai zermajmuhoi on (A, V, S va gayra)-ro dida mebaroem. Guftori zerin durust ast: agar teorema dar borai zermajmuhoi majmui M, ki tanho bo istilohoti amalhoi summa, burish va purkunanda bayon kard meshavad, durust boshad, pas teoremae, ki az hamin teorema dar natijai ivaz namudani amalhoi jam va burish muvofiqan bo amalhoi burish va jam, majmui kholii A bo tamomi majmui M, majmui M bo majmui holii A hosil meshavad, niz durust meboshad. Dar in mavrid purkunandai summa bo burishi purkunandaho, purkunandai burish bo jami purkunandaho ivaz karda meshavad.
Ad.: Efimov N. V., Visshaya geometriya, 5 izd., M., 1971.