Published online by Cambridge University Press: 20 November 2018
It is well-known that if is a quotient group of a group G, then (i)
is a partition of G, and (ii) the usual complex product (in the usual sense of multiplication of complexes) of every pair of members of
is a member of
. There arises the question whether, conversely, (i) and (ii), perhaps in a weaker form, suffice for
to be a quotient group of G.