Square Tiles (Large)

You sell geometric pictures. Each picture is made of 1x1 square tiles packed into a grid with no gaps. Here is one example.

.##..
.####
.####
.##..

Blue tiles are written as # and white tiles as .. You use no other color.

Some customers do not like blue and ask you to replace every blue tile in a picture with red tiles. Red tiles only come in the larger 2x2 size, which makes the job harder.

You may cover any 2x2 square of blue tiles with a single red tile, and you repeat this as often as you like. A red tile cannot overlap another red tile, it cannot cover a white tile, and it cannot stick out of the picture. Every blue tile has to end up covered. The picture above can be covered like this.

./\..
.\//\
./\\/
.\/..

One red tile is written as two / characters in its top left and bottom right cells, and two \ characters in the other two cells.

Given a blue and white picture, decide whether you can turn it into a red and white picture this way, and draw the result when you can.

The first line contains the number of test cases, $T$. $T$ test cases follow.

Each test case starts with a line holding $R$ and $C$, the number of rows and the number of columns of a picture, separated by a space. The next $R$ lines contain exactly $C$ characters each and describe the picture. # is a blue tile and . is a white tile.

Limits

• $1 \le T \le 50$
• $1 \le R \le 50$
• $1 \le C \le 50$

For each test case, first print a line of the form Case #x:, where $x$ is the test case number starting from 1.

If the blue tiles can all be covered by red tiles that do not overlap, print the finished picture as $R$ lines of $C$ characters each. Red tiles are written with / and \, white tiles with .. When a covering exists it is the only one, so there is exactly one correct picture.

If no covering exists, print a single line reading Impossible instead of the picture.