Mac Lane & Birkhoff 1999 do not explicitly define "reducible", but they use it in several places. For example: "For the present, we note only that any reducible quadratic or cubic polynomial must have a linear factor." (p. 268). Mac Lane, Saunders; Birkhoff, Garrett (1999), Algebra (3rd ed.), American Mathematical Society, ISBN9780821816462
Fröhlich, A.; Shepherson, J.C. (1955), "On the factorisation of polynomials in a finite number of steps", Mathematische Zeitschrift, 62 (1): 331–4, doi:10.1007/BF01180640, ISSN0025-5874, S2CID119955899
Fröhlich, A.; Shepherson, J.C. (1955), "On the factorisation of polynomials in a finite number of steps", Mathematische Zeitschrift, 62 (1): 331–4, doi:10.1007/BF01180640, ISSN0025-5874, S2CID119955899
Fröhlich, A.; Shepherson, J.C. (1955), "On the factorisation of polynomials in a finite number of steps", Mathematische Zeitschrift, 62 (1): 331–4, doi:10.1007/BF01180640, ISSN0025-5874, S2CID119955899