Questions regarding WSC round 4 - All 81

[Richard]

A bit of a pedantic question, but last year I didn't ask a pedantic question I thought of, and then people started writing negative numbers in their Sandglass puzzles and got away with it  
4.4 Hidden Skyscrapers Sudoku: 
I assume the rules want to express "All possible arrows are given"? The way it is written know you could take a cell with multiple arrows and leave out some, but not all of them.

Yes, that is what is meant here.

... visible in all directions of the arrow(s). Would be a better instruction?

No, the problem is more that you are grouping all arrows in a cell in the same single "if and only" statement. I would just slap "All possible arrows are given." on the end to make it water tight.

OK, I'll add that in the next version of the IB. (and competition puzzle of course.)