Indeed it is:

Code:

$ time sld grid-r
grid-r has 10 clues in 6 columns by 4 rows
initial grid
. . . . . .
c . . . . .
. . . . j .
. . q . . .
final grid - solved
o c c u r s
c r i n a l
t i n a j a
a s q u a t
real 0m1.700s

I came to a grinding halt on setting puzzles though. I can't do it yet and you can, which bothers me.

If, for example, I add one of the letters from A..Z into any blank cell of a blank grid, it takes me 26*cells to test all the alternatives. I can do that but I'm not expecting to find any more unique solutions with just one letter, not at the moment. That exploration takes about 10 minutes with my process in a 6x4 grid.

If I allow two letter permutations, it would take me of the order of 4 hours with 26*(cells)(cells-1) iterations.

Three letters is around 4 days. And so on. And that's just for a single grid-shape, 6x4, and there is a huge range of grid shapes to explore for unique solutions.

Is there a shortcut I'm just not seeing? or can I not exhaustively explore the full set of unique solutions.

Here's the simplest I can come up with:

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