The goal of this puzzle is to fill in every square with a red or blue piece, so that there are no lines of four pieces of the same color in a row, vertically, horizontally, or diagonally.
Click on a square to place a piece in a square or remove one. Squares with a grey background are clues and can't be changed. If you make a four-in-a-row, you will see a line through those pieces. If you solve the puzzle, a green border will appear.
All puzzles are randomly auto-generated and have a unique solution. There are three difficulty levels:
Easy can be solved with simple logic only, and has a lot of clues.
Medium can be solved with simple logic only, but has a minimal number of clues.
Hard requires more complex logic or guess-and-check, and has a minimal number of clues.
To try a guess, hit the Guess button, and it will keep track of the initial guess you make (green) and everything you can deduce from that (yellow). Then:
Click "Accept" if you think you made the right guess. You will keep everything you did in Guess mode.
Click "Reject" if you think you made the wrong guess. You will only keep the opposite of the initially guessed piece.
Click "Ignore" if you don't know if the guess was correct. You won't keep any of the guessed pieces.
This vevrsion is by Michael Gottlieb, 2017. I first saw this type of puzzle in the iOS app "Logic Games" by Andrea Sabbatini.