| http://www.w3.org/ns/prov#value | - Let and be topological Abelian groups and a quasi-homomorphism. (1) The sets form a basis of neighborhoods of zero for a group topology on .(2) If denotes the group endowed with the topology induced by the quasi-homomorphism and and denote the canonical inclusion and projection, respectively, is a twisted sum of topological Abelian groups.(3) A quasi-homomorphism is approximable if and only if the
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