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- [6] LIMIT-CYCLES OF QUADRATIC SYSTEMS COMPTES RENDUS HEBDOMADAIRES DES SEANCES DE L ACADEMIE DES SCIENCES SERIE A, 1980, 291 (05): : 337 - 340
- [9] A SUFFICIENT CONDITION FOR THE EXISTENCE OF LIMIT-CYCLES OF CLASS(II) OF QUADRATIC SYSTEMS KEXUE TONGBAO, 1983, 28 (08): : 1139 - 1139
- [10] ON THE NUMBER OF LIMIT-CYCLES IN QUADRATIC SYSTEMS VESTNIK LENINGRADSKOGO UNIVERSITETA SERIYA MATEMATIKA MEKHANIKA ASTRONOMIYA, 1987, (02): : 129 - 130