| 摘要 |
A rectangular sheet of paper or other foldable but inelastic material has its first fold (2) at an angle of 45 deg. to the middle of the long side. The second fold (4) is parallel, starting from the middle of the opposite side. The two flaps (6,7) meet at a seam. A third fold (8) at right angles to the second fold extends partly over the flap (6). The point (10) of the flap (9) reaches the stippled line (11). A fold along this stippled line brings the fold line (12) over to the fold line (8) to complete the envelope. |
