1. [Does a minyan say tachanun if there was a siyyum or if there is going to be after aleinu?](http://chat.stackexchange.com/transcript/message/5745882#5745882) Or, is it preferable to have a Siyum on Shabbat (just for example) to avoid this *safeik*?
2. Is Tachanun recited at a Siyum of all the Masechtot of Sha"S Bavli?

<http://en.wikipedia.org/wiki/Siyum>