Top op is a quasi-variety
Barr, Michael ; Pedicchio, M. Cristina
Cahiers de Topologie et Géométrie Différentielle Catégoriques, Tome 36 (1995), p. 3-10 / Harvested from Numdam
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@article{CTGDC_1995__36_1_3_0,
     author = {Barr, Michael and Pedicchio, Maria-Cristina},
     title = {$Top^{op}$ is a quasi-variety},
     journal = {Cahiers de Topologie et G\'eom\'etrie Diff\'erentielle Cat\'egoriques},
     volume = {36},
     year = {1995},
     pages = {3-10},
     mrnumber = {1322799},
     zbl = {0819.18002},
     language = {en},
     url = {http://dml.mathdoc.fr/item/CTGDC_1995__36_1_3_0}
}

Barr, Michael; Pedicchio, M. Cristina. $Top^{op}$ is a quasi-variety. Cahiers de Topologie et Géométrie Différentielle Catégoriques, Tome 36 (1995) pp. 3-10. http://gdmltest.u-ga.fr/item/CTGDC_1995__36_1_3_0/

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P.T. Johnstone (1982), Stone Spaces. Cambridge University Press. | MR 698074 | Zbl 0499.54001

M.C. Pedicchio (to appear), On k-pcrintitability for categories of P-algebras.