To truly be a logical puzzle, Suduku should only be solved by logical steps ( i do accept Nishio as a logical step, in that it is testing for a hypothese).
The difficulty which I have is that among the range of technics available, it is sometimes difficult to select the appropriate one.
I have come across numerous puzzles which require sophisticated solving technics.
The problem is that the selection of the technic is not a logical step.
When I am stuck, I usually check for:
1. X-wing
2. Swordfish
3. Colour
4. Nishio
This sequence has led me in numerous difficulties ( in various puzzles) because although all conditions were right for using sworsdfish (i.e all the candidates were identified), I still was unable to solve the puzzle.
This suggests, that not only the solution of a sudoku has to be unique, but also the sequence of technics to solve it.
I am not comfortable with that conclusion