 Ordinal rank function for a relation (source code)

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= Ordinal rank function for a relation
{title2=$\rho:X\to\operatorname{Ord}$}

An ordinal-valued function strictly increasing along a relation. For a well-founded set relation, or a <set-like> class relation, the canonical rank is $\rho(y)=\sup\{\rho(x)+1:xRy\}$.

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