I am looking for a definitive answer, a solid proof (in your view): Have we been visited by aliens or not?

Okay, chances are mathematically significant that in this vast Universe there must be other life forms out there besides us - intelligent or otherwise. ... But my question is: Do you think we have been visited by some of those aliens, and if so on what facts do you base your umption / knowledge (besides hypnotic regression evidence proffered by the supposedly abducted, I mean)? ... Can you, for instance, name a well-doented and generally accepted case? … Serious answers only, please.