Find here the riddle by Vienna Center for Logic and Algorithms (VCLA) at the at the ball: Ppen the doors to other dimensions – with logic. Help alchemy find its way into the world of modern science by solving the puzzle. Your task: fill in the grid with the four alchemical symbols for earth, fire, water and air, such that the same symbols never touch each other, not even diagonally, by putting exactly one symbol in each rectangle, no matter the size of the rectangle. The puzzle was created especially for the Vienna Ball of Sciences by Maarten Löffler, University of Utrecht.

 The Vienna Center for Logic and Algorithms (VCLA) is a competence center at the Faculty of Computer Science of the Vienna University of Technology. It was launched in 2011 to r aise awareness of the importance of logic and algorithms – both in the scien tific and general public. www.vcla.at / Twitter and Facebook: @vclaTUwien

And here is the solution: