●部分を平たい面にする(A)

Make the ● part flat (A)

Open the folds marked with ● in the left image, flatten the folds, and create a flat surface like the one in the right image.
An example of the specific steps is shown in the following image.

1 Stand the front right piece of paper up in the center.
2 Hold the two folded edges of the paper with your fingers, overlapping each other, at the ▲ part on each side, and slowly pull the paper left and right to open it.
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4 Once the paper is fully opened, align the left corner B with A and fold the left CD.

5 Make a crease in the CD and return it to its original position.
6 Fold the right side of the CD, aligning the right corner B with A.
7 Make a crease in the CD and return it to its original position.
8 Make sure to fold along the mountain and valley fold lines in the diagram.
Next, pinch the ▲ parts with your fingers on both sides and move them towards the center, and the paper will fold itself in as it goes along.
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11 Make the ● part flat (A) is complete.