solving a super fearsome Sudoku

There are many different ways to solve a Sudoku. But I find the best strategy is to use pencil markings to denote the only possible 2 candidates (numbers) that can occur in each 9 box frame. How you do this is to begin with number 1 and then all of the numbers up to 9 by inserting pencil markings where only 2 candidates can reside in any 9 box section.

That is after firstly marking in the more obvious cell solutions from the given numbers of the puzzle. That approach I find is the most efficient strategy to uncover the hidden doubles and logical solutions that enable one to quickly crack open the puzzle.   
Below is a super fiendish Sudoku taken from The Times newspaper which represents the most difficult level amongst all published Sudoku’s published in Britain.    
But if you are a slow thinker like me it might take an hour or more.  I have included it here should you like to give it a try. Just plug in the numbers and see if you can solve this difficult puzzle.   

You can ascertain how long it takes you and then refer to the link for the step by step solution or alternatively for a solution should you get stuck. The link is to an ex world champ demonstrating how such a difficult puzzle can be solved in under 5 minutes.

Down under I have worked our why the latest Age newspaper Sudoku’s (rated the most difficult on a scale of 1-5) are on odd occasions incapable of logical solutions. What I mean by that is they can only be completed by a number of guesses at critical points and have a number of alternative solutions.   

The first clue came from watching on u tube an ex world champ solve a Times fearsome puzzle. Whilst demonstrating his logic using pencil marks, he reached a point in the puzzle where it appeared there were two equally valid solutions. 

But he remarked that only a properly constructed Sudoku would appear in the Times. Armed with that technical knowledge he sought a solution elsewhere in the puzzle. In other words the puzzle must have only one logical unique solution for those published in the Times.  Sure enough he was able to solve it logically.  

But in the Age I have tested out Sudoku’s, which were brutes of puzzles (that is those of 5 star ratings which is the highest difficulty as the easiest is a 1) only to find some were invalid Sudoku's. The proof was demonstrated as per the On Line Solver, which informed they were invalid Sudoku's.  

I fed in the opening numbers and clicked on the check button to be told as much. On one occasion the website provided 7 different solutions none of which were based in a logical progression. 

So this last Saturday I plugged the initial numbers from the Age to check before I started. Sure enough it confirmed that this was a logical puzzle with only one unique solution. Hence I was able to complete it.

What you could do if you like is to plug in the numbers from this site as I intend, each time, just to make sure it is a valid puzzle. I might even write a complaint letter to the Age, who are rather obviously sourcing their puzzles from sources that don't comply with this given integrity. Here is the second reference website as per below in case you also like the idea 

https://www.youtube.com/watch?v=nrz4rhbaVR0


https://www.sudoku-solutions.com/

		3
				3
2			8		6	7
6		4	3	2		1
		7	5		1		4
5				9	4	8
				4	7			5
4
	8		9		3	2