is allocated to protect against the failure of fs; vg and q units
of flow to protect against the failure of fv; tg (shown in Fig.
1c). If after some disruption either of the fs; vg edges fail, 1
unit of flow will still remain from s to t. By fully protecting the
primary fs; vg edge, there is zero probability that its failure will
cause the flow to drop below the full demand. The probability
that the flow will drop below 1 after some failure is 1
4 , which
meets the MFP requirement. This routing only needs 3 + q
units of capacity, as opposed to the 4 units that full protection
requires.