Terry, here's a reply from

anyone.

terry wrote:But what if we try a nine in r3c2. WE can still come out with a No for r1c6 being No 7 in this case I think...

I think not! Did you miss this?

simes wrote: r3c2=2, r1c3=9, r8c3=8, r8c4=3, r8c6=9, c7c6=7, r1c6=3

or

r3c2=9, r5c2=3, r5c8=7, c3c8=3, r1c7=7, r1c6=3

It's funny that you managed to follow all the steps except for the last line –I thought the last line was pretty straightforward once you’d eliminated candidates via all those steps.

terry wrote:teh chains you talk about are only a guessing game

It's trial & error but it's not guessing - if two chains from the same cell lead to the same answer in another cell by different loops then you have a

proof, not a

guess. It's only guessing if you don't check both loops. simes' chains led to a

proof for r1c6. My chains were a lot longer but didn't require the colouring step - they led to a

proof for r6c1.

With a valid puzzle you never need to ‘take a punt’ as you put it and you will never be in the position of finding out later in the puzzle that you made a wrong move. Every number you enter is the one and only number for that cell, otherwise you don’t enter it.