English
If Module.Free R M holds, then the index type ChooseBasisIndex R M indexes a basis for M.
Русский
Если Module.Free R M выполняется, то тип ChooseBasisIndex R M индексирует базис для M.
LaTeX
$$$$ \text{ChooseBasisIndex }R M := \text{the index type of a basis for } M $$$$
Lean4
/-- If `Module.Free R M` then `ChooseBasisIndex R M` is the `ι` which indexes the basis
`ι → M`. Note that this is defined such that this type is finite if `R` is trivial. -/
def ChooseBasisIndex : Type _ :=
((Module.free_iff_set R M).mp ‹_›).choose