is that a fact

Also, is that so? Phrases indicating that one is following what another person is saying. These expressions, which require no reply, can be used either straight-forwardly, as in You mean you've flown to Paris three times just this month? Is that a fact? or sarcastically, expressing disbelief or contempt, as in Just wait, I'll be promoted over you before the year is out.? Oh yeah, is that so? [Late 1800s]