In 1975, Cresp and Sullivan described all rings which satisfy
certain conditions on their multiplicative structure: in particular,
those rings
for which every multiplicative endomorphism
is an additive endomorphism. In 1977, Sullivan proposed an alternative
problem: describe
all rings for which every additive
endomorphism is a multiplicative endomorphism, and later several
authors referred to this as 'Sullivan's Problem'. In this talk, we
discuss some attempts to solve this problem using abelian group theory,
and we suggest there may be a better approach via semigroup theory (as
originally intended). |