thanks :-) happy you've been able to try it
And - yes - this Happy Days episode was the first time Mork was shown on screen - Robin Williams was more or less a last second random choice because the designed actor refuse to do that part. He was *brilliant* everybody loved him and everybody praised him - and few days after he was contacted for the first time by a big name for acting (and then he was proposed to do a his own spin-off series called Mork and Mindy). That's more or less the history behind.