none of Gordon's 17s is solvable with naked singles alone.
The 18 was found after examining about 10million out of the
14million 18s by adding a clue to a 17.
So these are very rare and I was indeed surprised when it
popped up after 10mio examinations.
About half of the 17s can be solved with naked+hidden single,
which is also easy.
Hidden single is even easier usually as pointed out.
So you should try to solve my puzzle with
naked singles only.
