@ZachHauk Here's one that I think should be easy, but I'm not quite sure how to do it.
Suppose you have an infinite chessboard, with some squares painted blue, some squares painted orange, and some left unpainted. Suppose that no blue square is adjacent to an orange square (not even diagonally).
Also, suppose there are squares labeled X and Y. Suppose there's a path between X and Y that avoids blue squares (only goes through orange and unpainted squares), and a path between them that avoids orange squares. How can we prove that there's a path between them that avoids both colors (only goe…