The Sudoku variation in question turns out to be called
along with some aliases,
and cells 1– 8 by themselves
can force a unique solution without being given cell 9.
revealed how delightful this puzzle is
but I had forgotten the details months later
when mentioning it to a fellow Sudoku enthusiast,
so some variety ensued.
The layout on the left, with straightforward numbering,
has a very sleek route to solution 2
whereas the numbering on the right demonstrates that
an irregular set of initial numbers
can also force a unique solution
and be amusing to solve 3
if you’re in the mood.
Progress came from starting with small boards while experimenting with
simple zigzags and L shapes.
The 4×4 and 5×5 layouts along the way
were misleadingly efficient 4
and led to an unnecessarily awkward 9×9 layout.
Footnotes (solutions of layouts):
Synopsis of the three stages in
(Circles ◯ spotlight cells that were most recently filled
or are immediately determinable at the steps shown.)
First and last steps of the present straightforward solution.
(Circles ◯ mean the same1 as above.)
Synopsis of a solution for irregularly placed initial numbers.
(Circles mean the same1 as above.)
Solutions of the 4×4 layout in just two steps
and of the 5×5 layout in four steps.