If a fast day which normally falls out on shabbos is pushed off, such as the 17th of Tammuz, and a person fasts on that shabbos for another permissible reason, such as a taanis chalom (fast for having a bad dream) is that person exempt from fasting the following day - ie the nid'che 17th of Tammuz fast?
- Anybody can ask a question
- Anybody can answer
- The best answers are voted up and rise to the top
The Ben Ish Chai in Rav Pealim (chelek alef question 29) cites the masat binyamin among others as indicating that you would have to fast on 17 Tammuz because anyway a person is obligated to fast a second time for having violated oneg shabbos by fasting on shabbos - even though he is permitted to fast for a tanit halom. See Orah Hayim 288