An ע"א will prove; for he is included in the rule of הכחשה והזמה, etc. - עד אחד יוכיח שישנו בהכחשה ובהזמה
Summary:
There is no הזמה by an ע"א because of the weakness of an ע"א that he is not מחייב ממון. Therefore we consider that an ע"א is ישנו בהזמה. However concerning a פירכא on the מה הצד of פיו וע"א (that they are not בתורת הזמה), there is a dispute whether this is considered a valid פירכא כל דהו or not; since an ע"א is not משלם on account of his weakness.
And the תנא תונא is referring to the other ר' חייא. We are witnesses that whatever this one holds, etc. - ותנא תונא אאידך דר' חייא. אנן סהדי דמאי דתפיס האי כולי
Summary:
According to רש"י the ותנא תונא proves that there is a שבועת מוב"מ by הילך from the fact that there is a שבועה in the משנה even though the משנה is a case of הילך. However
תוספות rejects this for if the שבועת המשנה is on account of העדאת עדים so there is proof for ר"ח קמייתא as well.
תוספות explains that מאי דתפיס is equivalent to a הודאה במקצת. The שבועת המשנה is then (similar to) a שבועת מוב"מ when there is הילך. There is no proof however to רח"ק. The גמרא at this point already knew that the משנה is a שבועה דרבנן, however if הילך would be פטור there would be no שבועה דרבנן by הילך. The difficulty that remains is that according to the גמרא there is no proof for רח"ק because כי היכי דאנן סהדי להאי. However according to תוספות there is no proof to רח"ק because תפיס is הודאת בע"ד not העדאת עדים.
And we derive from this that הילך is פטור, etc. - ושמע מינה דהילך פטור
Summary:
According to רשב"א there is no מיגו of שתים (even if שתים is פטור because it is הילך), for שתים is considered a כוה"כ (on account of הילך); however ר"ע maintains that the כוה"כ in this case is not a מעיז since the שטר supports him.