When is the space of semi-additive functionals an absolute (neighbourhood) retract?

Abstract

In the present paper proved that if for a given compact Hausdorff space X the hyperspace exp(X) is a contractible compact space then the space OSf(X) is also a contractible compact space. As a consequence it is established that the space OSf(X) of semi-additive functionals is absolute (neighbourhood) retract if and only if the hyperspace exp(X) is so.