Editing Sudoku/Thorkil Naur (section)

== Field reduction and element reduction produce identical results ==

It has come as a significant surprise to me that the two reduction
strategies, although they certainly appear quite different to me,
nevertheless produce identical results. At least in the practical
circumstances of solving real SuDoku puzzles. And since field
reduction is much faster than element reduction, the present version
of the code uses field reduction only to find the final solutions:
The call of sdkSolve in sdkProcessSuDoku uses by=sdkReduceByField.
The element reduction code has been retained, however, for possible
further experiments.