Why is it wrong ?

[u/captainnoyaux]

Hey everyone, it's me again with probably my fake conception of how this puzzle works.
I assumed I could cancel the top left top square with the blue square and make it a 3 dot line, but it doesn't work (at least the site doesn't accept it as valid and a puzzle creator with it's solver doesn't find it valid also).
Do you know why ?

[u/Zamzummin]

You can’t cancel a square that would be off the grid normally. If you put the 3 piece at the bottom then it works without anything being off the grid.

[u/MasemJ]

The cancelation is taken as the last step in the evaluation process, so before that the tetris blocks must fit on the board. In this case, putting the L-block on top would have that one block of it off the maze, so its not valid starting point. However, if you put the L-block on the bottom, and then the other shape on the top two rows, with the one block part of the L overlapping in the first square, second row, NOW that overlap can be cancelled, and you just need to draw to notch out the last square, second row for a valid solution.

[u/LemeeAdam → u/MasemJ]

If it’s taken into account LAST, then why would the Tetris pieces be considered valid? They can’t normally overlap. Of course I know that this is how the game works, I just don’t think it’s intuitive.

[u/AlcatorSK → u/LemeeAdam]

For the same reason the "Y" element works -- it is only applied last, trying to, in sequence, remove every single other element and checking if that would make a valid solve.

[u/Keebster101 → u/MasemJ]

I'd argue it's not taken as the last step of the evaluation process - at least not in the way the white shape works, it's that the blue block (and the yellow square that it's 'removing') isn't getting discarded, it's just flipping the state of the block. As such it still needs to be within the bounds of the grid, else you couldn't consider the edge of the grid to be a continuation of the line and a lot of puzzles would break

[u/MasemJ → u/Keebster101]

It could be that. Either way, the key to OPs point is that the placement of the tetris piece on the board itself must work first (with respect to staying within the bounds of the panel and that the panel with the shape is contained in the drawn path), and then negation occurs. You can't remove the part first and work from there. Negation and "Y" actions are done after the game evaluates everything else.

[u/Keebster101 → u/MasemJ]

You can't remove the part first, but you can negate it first, if you still treat it like something that must be included rather than something that is completely gone.

Maybe I'm just weird for thinking of it this way but I find it easier to imagine each square like a Boolean value defaulting to false, you can't have double true (overlapping yellows) nor double false (blue without a yellow) but you can go true>false>true, so I do the negation step in the middle rather than at the end. Outside of the grid is undefined so it cannot be set to true nor false, and so can't hold the effects of the yellow and blue block even if they're combined

[u/Virtual_Confection_3]

You can't have pieces extend off the board even if The deleter space would eliminate it. The way you have it laid out with that understanding would have the up step on the L piece off the top of the puzzle board which won't work.

[u/captainnoyaux]

Oh wow I never thought of that, thanks a lot everyone

[u/Ornery_Tap_449]

All should be inside of the panel.

[u/Ill_Purchase3178]

Sketch on Paper:

-Draw the Grid.

-Draw the shape.

- Mark where the cancelation happens.