Let’s say that someone, for whatever reason (say he forgot it was Behab), accepted upon himself to fast Behab but didn’t fast one of the days (say, for instance, he fasted Monday but not Thursday).
- Does he have to make it up by fasting another day?
- If so, does he make it up on a specific day (ex. the Thursday following the second Monday of Behab), or can he make it up on any weekday? Does he have to start over from the first Monday to complete a full set of Monday-Thursday-Monday?
- If a full minyan managed to miss a day of Behab davening, do the above rules apply for them to make a minyan for Selichos?