The Gemara [Ksuvos 9a] says that if one claims פתח פתוח מצאתי and there is only one ספק [such as that she is the wife of a Kohen so the only ספק is whether she had ביאה while תחתיו], he is believed - see there [if you went to yeshiva long enough you spent weeks or months on the sugya...]. Says Tosfos - The Gemara seemingly missed a ספק, namely maybe she was a מוכת עץ and that would explain the open door!!?? The answer is that since she didn't make this claim in her defense we don't entertain that doubt.
Asked the Maharsha - She should be believed to say בתולה הייתי with a מיגו that she could have said מוכת עץ אני??
He answers that we don't say מיגו באיסורים.
Question: When a man says I divorced my wife he is believed b/c he could divorce her if he so chooses and this is a מיגו. Namely, he is believed that he divorced her מיגו that he can go ahead and divorce her if he feels like it, so why should he lie??!
So we see, NOT like the מהרש"א, that we DO say מיגו באיסורים?!!!
OK. LOTSSSSSS to say. בעז"ה ועוד חזון למועד.
