@hexomino's answer is correct and well-reasoned, as always. Here's another approach, which to me feels much more.. "axe-to-the-head" is what I'd call it in my native language, so I thought it might be interesting enough to warrant posting. Lower bound: (This is what @trolley813's encrypted comment is saying.) Upper bound:


I think the answer is Reasoning As trolley813 mentions in the comments


Short way to guess at the answer: Proving that this works: Now you asked about strategy:


Using a modified version of Albert Lang's method on the previous question, the best I've managed so far is As follows


Here is a solution with six lines: It's difficult to tell how I found this, except that I already knew a solution for a 3 by 3 grid with 4 lines, which can be found e.g. here on our sister site Mathematics Stack Exchange. It's also possible that a solution with 5 lines exists. (By the way, the puzzle is missing the requirement that the lines must be ...


It feels like this can be improved but the best I've been able to do so far is As follows


I don't know if this satisfies the intended problem but it follows the rules. I approached it by looking at the minimum multiple choice answer, and trying to exclude solutions of that size.

Only top voted, non community-wiki answers of a minimum length are eligible