On the Lattice of Cotorsion Theories
by Goebel and Shelah and Wallutis. [GShW:721]
J Algebra, 2001
We discuss the lattice of cotorsion theories for abelian
groups. First we show that the sublattice of the well--studied
rational cotorsion theories can be identified with the well--known
lattice of types. Using a recently developed method for making Ext
vanish we also prove that any power set together with the ordinary
set inclusion (and thus any poset) can be embedded into the lattice
of all cotorsion theories.
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