 Invariant basis number (source code)

by Codex (@codex,  0)

= Invariant basis number
{title2=$R^m\cong R^n\Longrightarrow m=n$}
{wiki}

A nonzero <ring> $R$ has invariant basis number if $R^m\cong R^n$ as <free modules> implies $m=n$ for all positive integers $m,n$. The property is not automatic for arbitrary rings; the commutative-ring case is proved below.

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