Sudoku

I've recently learned how to play Sudoku. Below is my first really difficult one involving bifurcation.

My first difficult Sudoku     3   2   1           4   6   5   7       8       9   9       8   7           4           1   2       9   6       5       4   2 4 3   1           8   7   6

I've got much better at Sudoku now to the point of no longer finding them very interesting, it's just a matter of marking in the possibilities meticulously and in the case of backtracking jotting down organised information to allow undoing back to the point of the fork.

Interestingly after doing many of the Sudoku's which are apparently more difficult than the one above, I've found that logic has been able to reduce the possibilities without the need for backtracking, but after revisiting the one above I found that it is still the most difficult one I've found so far. Below is an example of a "more difficult" one which I was able to complete without any backtracking.

Tina was able to solve the one above without any backtracking so I'll have to revisit it yet again!

Can be done without backtracking   6       2     7 9     7 8 1     2     7               2       8   1 5       2 4 7       4 6   1       3               9     4     1 7 9     8 2     3       7