Logical. Tested.
The mouth here is the sort of thing I was referring to in the description in Part 2.
This is the reason that symmetry is not an assumption but a logical certainty if the puzzle has only one solution.
You do not have to "try all options" (using temporaries or otherwise), as symmetry IS the logical deduction.
If you don't read over these things, then I'll have to do something to get your attention.
I'm still skeptical about considering that symmetry may be considered as a certainty and not an assumption under conditions proposed by BaggyT. I'm going to think about it more profoundly.
Here, I didn't need to use symmetry as a certainty or an assumption : this hanjie may be resolved logically because the 4 and the two 1 that remain are making a layout called "in smile" or "in mustache" which is typical : if the 4 begins too much on left or too much on right, you can't place the two 1. So there is only one possibility determined logically.
pas mal... pas mal...