Q) If the most recent interval between two periods [haflogo] was shorter than the previous interval between periods – which of the intervals should I keep as veses haflogo?
A) The situation you are describing is classically referred to as veses k’tzoro okeres aruko – i.e. a longer interval [between two periods] followed by a shorter interval [between two periods]. We find in the Poskim two main conflicting opinions about this scenario:
- The Remo[1] and Taz[2] both maintain that a short interval cannot affect, or interfere with, a long interval. This is because there is a general rule regarding all vestos that the only way that a veses can be eliminated is by the absence of a period on that yom haveses (which is proven with a bediko), or that another veses has become veses kovu’a. Otherwise, a veses will remain in effect until it is eliminated.
Therefore, in this situation the original, longer veses cannot be affected by a shorter interval, and remains in effect until it is eliminated.
- The Shach[3] contends that a shorter interval will eliminate the previous, longer interval, and one only needs to be concerned with the most recent interval.
- Many Poskim[4] follow a variation of the first opinion and maintain that a lady whose most recent interval is shorter than the interval preceding it should be chosesh for both This is because the longer interval is still in effect, in addition to the current, shorter interval, and both intervals are calculated from the date of the last period.
This seems to be the general consensus among the Poskim.
Therefore, if a longer interval [halflogo] is followed by a shorter interval, one should ideally calculate, and be choshesh for both intervals – from the date of the last period. Rav Mordechai Eliyahu maintained that Sephardim can follow the opinion of the Shach (that the shorter interval will eliminate the previous, longer interval).
[1] קפ”ט י”ג
[2] יו”ד קפ”ט ס”ק י”ח
[3] קפ”ט ל”א, מ’
[4] כו”פ, סד”ט, גר”ז, בית מאיר, לחם ושמלה