My pop up card uses the similarity of rectangle. Two geometrical objects are called similar if they both have the same shape, or one has the same shape as the mirror image of the other, and one can be obtained from the other by uniformly scaling: enlarging or reducing, possibly with additional translation, rotation and reflection. Fold the paper in half vertically, after get one line trace in the middle, fold the paper two times based on the line in the middle of the paper. And cut 1 centimeter on the top of the paper in horizontal, then open the paper and push the middle section to the inside. Cut 2 centimeter under the one-centimeter line, open the paper and push the middle section to the inside and get two traces each side, repeat the first
