## Archive of Superior puzzles published in the Sunday Times

All about puzzles in newspapers, magazines, and books
Looks like my post got lost. Here goes again...

Thanks for the info, I didn'r realise that the technique I used was known as a forcing net. The logic is absolutely water-tight and from a strict mathematical stance using "if x; if ¬x" logic is what's necessary to prove the x-wing dispite wrapping the proof in language that appears not to do so. So I don't see how forcing net can seriously be regarded as invalid. But I guess there nothing wrong with adding additional constraints to the puzzle. Since we've debated this recently there's no need to repond further on this point.

By the way, what did you mean by "solving withou PM"?

Richard
richardm

Posts: 53
Joined: 27 December 2006

### re: "solving withou PM"

richardm wrote:what did you mean by "solving withou PM"?

some (such as myself) prefer solving without "pencilmarks"
i.e.
without writing the list of possibilities in each cell

Pat

Posts: 3690
Joined: 18 July 2005

richardm wrote:Thanks for the info, I didn'r realise that the technique I used was known as a forcing net. The logic is absolutely water-tight and from a strict mathematical stance using "if x; if ¬x" logic is what's necessary to prove the x-wing dispite wrapping the proof in language that appears not to do so. So I don't see how forcing net can seriously be regarded as invalid. But I guess there nothing wrong with adding additional constraints to the puzzle.

If you'd read my reply carefully you'd have realised that I never regarded your method as "invalid"... In fact I agreed very much it's logically water-tight and that's why I described the move using our conventional "lingo" to demonstrate it's validity to anybody who didn't follow it (in case)...

I just wanted to state the fact that some people might not like to use moves like this because they sort of feel like trial and error... It's just a matter of personal preferences, irrelevant to the logical validity of the move (because trial and error is definitely one of the logically valid ways to solve a puzzle)...

richardm wrote:Since we've debated this recently there's no need to repond further on this point.

I don't see it as a debate and I'm not participating in any argument anyway (i.e. not convincing other people which way is better)... Just want to clarify my point...
udosuk

Posts: 2698
Joined: 17 July 2005

So what did you mean by PM?
richardm

Posts: 53
Joined: 27 December 2006

### Re: re: "solving withou PM"

richardm wrote:So what did you mean by PM?

udosuk

Posts: 2698
Joined: 17 July 2005

Sorry, yes I missed it. And yes I do like soving without PM. If I have to resort ot PM I regard the challenge as lost.

Richard
richardm

Posts: 53
Joined: 27 December 2006

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