Upon what is dependant the machlokus whether one says Lamnatseiach in Shachris after the 2nd Ashrei on Isru Chag?
Answer
Most Poskim rule that one does not say Lamnatzeiach on Issru Chag, because it is a Yom Tov.
However, Sefer Haminhagim (R’ Avraham Childik, 14th century) quotes R’ Yaakov be R’ Natan as ruling that one does say Lamnatzeiach on Issru Chag, and adds a rule that whenever one says Hallel one does not say Lamnatzeiach.
