et

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$($G$,$s$,$t$,$c$)$ be a flow network,

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G$=($V$,$E$).$ A directed edge

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e$=($u$,$v$)$ is called always full if

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f$($e$)=$c$($e$)$ for all maximum flows

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f; it is called sometimes full if

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f$($e$)=$c$($e$)$ for some but not all maximum flows; it is called never full if

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f$($e$)$