Where’s the fish?

A colleague shared with me the link to this Einstein’s riddle.  It looks easy at first, but it actually isn’t.  I’ve tried a couple of different models to solve it, but haven’t figured it out yet.  Something tells me that if I remembered Prolog from my college days, I would have solved it in about 3 minutes.  But I don’t.  So pieces of paper and text files it is.  If that won’t be enough until lunch time today, I’ll start doing something in PHP or Perl…

 

Update: Solved it!  My initial model of addition wasn’t right. Subtraction worked much better.