# Recursion (Solitaire XXV)

Time for another Isolation Puzzle while the days grow darker. Here are all 30 squares whose sides are colored in four different colors, chosen from five available colors. Print and cut them all out:

Pick one of them. The first easy puzzle is to assemble it using four of the remaining 29 squares, like so, for instance:

Notice that the border of the 2×2 square matches the border of the chosen square, and squares that touch must match along their common sides, too. The second not quite so easy puzzle is actually four puzzles, namely to assemble each of the four squares on the right using 16 of the remaining 25 squares. No duplicate usage is allowed! Below is a solution for the top left square.

Do this with the other three squares. The solution is by no means unique, and it is well possible that you get stuck and have to revise your choices. When done, you are left with 9 remaining squares. The final not at all easy puzzle consists of assembling them into a 3×3 square so that the sides are in one color each, and again tiles match their colors along joint sides. Like so:

In the above example (yours might well be very different), can you also have dark green occur on the sides of the 3×3 square? And, has this anything to do with dark green missing in the square we started with? Sometimes the past is going to haunt us…

And finally (but maybe this is impossible), can you make the 3×3 square so that its border is an enlarged version of the square we started with?