Source: 2015 WSC, Sofia
Potential issue: repeated digits. This question already raised from other threads, but here it is a bit more extended, with a digit repeated 4 times.
1234 Sudoku [WSC 2015]
Re: 1234 Sudoku [WSC 2015]
A definite no for me - not only have you got the repeated numbers having to be placed, there is also something of a Heyawake or Hitori like constraint in terms of packing the 4's and 3's into fairly limited regions.
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