twin3

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  d4 = 12.  d9 = 127.
  
  On row d 1 and 2 occur only in cells d4 and d9.
  
  So these two cells monopolize 1 and 2
  
  and so d9 cannot be 7.

       1         2         3          4         5         6          7         8         9       
  .---------.---------.---------..---------.---------.---------..---------.---------.---------.  
a |123      |         | 23      ||123 5    |         |         ||         |1   5    |         | a
b |         |         |         ||         |12 4     |12  5    ||12 45    |         |12 45    | b
c |123      |         |         ||1234 6   |12 4 6   |123      ||         |1  4     |         | c
  |---------+---------+---------++---------+---------+---------++---------+---------+---------|  
d |     67  |     6  9|      7 9||12       |         |         ||         |         |12    7  | d
e |  3 5  8 |         |  3    8 ||         |1      8 |         ||1  45    |         |1  45    | e
f |    5 78 |         |         ||         |         | 2     8 || 2  5    |         | 2  5 7  | f
  |---------+---------+---------++---------+---------+---------++---------+---------+---------|  
g | 2  5678 |    56   |         || 23456   | 2 4 678 | 23 5  8 ||         |   45 7  |  345 7  | g
h | 2  5 7  |         | 2    7  ||12 45    |12 4  7  |         ||         |1  45 7  |         | h
i |         |    56  9|      789||1 3 56   |1    678 |1 3 5  8 ||1   5    |         |1 3 5 7  | i
  '---------'---------'---------''---------'---------'---------''---------'---------'---------'  
       1         2         3          4         5         6          7         8         9       

  This deduction occurs very rarely.

  At this point I cannot see anything to do, so I would guess.
  
  Can you see what to do?