First, I think your equation (4) contains at least one error. The x factor from (2) went missing.
Second, your statement of the condition in (2) does not make sense. You are trying to turn on (or off) a constraint involving the summation over fl indices based on the value of \mu_{fl} for a single fl index (which one?).
So the first step is to repair/clarify the question. You might want to post the revised question on OR Exchange (
https://www.or-exchange.org/), which gets a lot more traffic these days than sci.op-research does.
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