Alternate characterization of rank
Let
- Suppose that
has rank and is a maximal linearly independent set of elements in . Let be the submodule generated by . Prove that and is a torsion -module. - Conversely, prove that if
contains a submodule that is free of rank such that the quotient is a torsion -module, then has rank .
Hints
- Show that for any
there is a nonzero such that for some . - Let
be a set of elements of . Find some nonzero so that can be written using a basis for . Then show the (and hence ) are linearly dependent.