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4. 4. J. W. Alexander, Sur les cycles des surfaces algébriques et sur une définition topologique de l’invariant de Zeuthen-Segre, Rom. Accad. Lincei Rend. 23 (1914), 55-62.
5. A proof of the invariance of certain constants of analysis situs;Alexander, J. W., II;Trans. Amer. Math. Soc.,1915