(10 years ago) Fantastic level ! Took me over 80 tries and even after I solved it, it ain't clear to me, WHY this is the fastest way to do it ! !! Excellent and very interesting. P. S. Was 4 off, for a loooong time.
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EDIT 2023, 13th May: same old story, only that this time it went faster. First I was kept 4 off, then somehow got to 2 off, was kept a bit there and then I found it. The saddest part is, that it is still not completely clear to me, why that was faster. :/
Did it really fast, only a bit more than a couple tries. As a result, I demoted it from professor to PhD. This puzzle is good, though I'm surprised to see it so high up.
Insights