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Published online by Cambridge University Press: 20 November 2018
In [3] D. B. Fuks defined a duality of functors in the category  of weak homotopy types. In general this duality is more difficult to work with than the duality of functors of the category
 of weak homotopy types. In general this duality is more difficult to work with than the duality of functors of the category  of pointed Kelley spaces [2]. It happens however that all so-called strong functors [2] F of
 of pointed Kelley spaces [2]. It happens however that all so-called strong functors [2] F of  induce functors
 induce functors  of
 of  , and if we denote the duality operators of
, and if we denote the duality operators of  and
 and  by
 by  and D respectively, then there are many cases where
 and D respectively, then there are many cases where  .
.