
22may24) note: 
this idea superceeded by revised KeyCell algorithm
which, essentially, does this routinely prior
to resorting to more elaborate methods...

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This is simple & general. It will ID "hidden" singles.

my Z2 Algorithm:
.) pick cell with only 2 candidates.
.) assert 1 then fully flush
.) find any resulting new singles; put into set A
.) restore assert, then assert the other, fully flush.
.) put resulting new singles into set B
.) restore assert.
.) let C = intersection A, B
.) any and all digits in C should be asserted. To
	facilitate that, simply remove all other
	candidates in the same cells so that the
	draw routine will color them green.

See asud-getkey* line 1095 (key_x) for a model
of what to put in getkey*.

