SUDOKU
  Most of these are from the guardian.
  www.puzzler.co.uk/guardian


#example
  ....834..
  3....4821
  7........
  ..94.1.83
  .........
  46.5.71..
  ........7
  1253....9
  ..724....

#wiki  hard
...1..74.
.5..9..32
..67..9..
4..8.....
.2.....1.
.....9..5
..4..73..
73..2..6.
.65..4...


#ec1
8...6..34
4.....2..
.7...5...
..5..7..9
...2.8...
6..9..1..
...3...8.
..7.....5
12..4...6

#ec2
...9.8...
..4...6..
.9..3..7.
9..2.4..6
..1...5..
3..8.6..2
.6..7..3.
..8...2..
...1.5...


#ec14  hard
..1.9....
.2...8.6.
..3...7.5
.4...6...
5.......6
...1...7.
6.8...4..
.7.9...3.
....1.2..

  find at about 160000 positions
  ..1.9....|761593842
  .2...8.6.|925478163
  ..3...7.5|483261795
  .4...6...|147356928
  5.......6|592847316
  ...1...7.|836129574
  6.8...4..|618732459
  .7.9...3.|274985631
  ....1.2..|359614287

#ec15    examine 42383 positions
5....2..8
..6...3..
.7..1..4.
...3....1
..8.4.6..
2....1...
.1..8..2.
..3...5..
9..4....3

#ec16
.....178.
.962....4
.1......5
.7...9..6
.........
3..5...2.
8......9.
5....813.
.247.....

#ec17     test around 150000 solutions
1...6..2.
...3..8..
.4...5..9
3......6.
..8...1..
.5......7
2..8...3.
..5..1...
.9..5...6

#ec19    try 353084 solutions
.4..52...
8.....3..
9.....7..
.27..6...
.........
...7..84.
..3.....6
..5.....2
...94..7.

#ec20 (353084)
..7..8...
.1....3..
...4....9
.8..9...6
.2.....7.
5...3..4.
9....6...
..4....1.
...2..8..

#easy
.1.42...5
..2.71.39
.......4.
2.71....6
....4....
6....74.3
.7.......
12.73.5..
3...82.7.


#001
8...7...2
..64.28..
.5..3..1.
.1.5.4.2.
2.5...6.7
.3.2.7.5.
.2..1..3.
..97.34..
3...4...8