| 摘要 |
<p>A print of this invention has a color-forming area and a dlscoloring area. The color-forming area is printed by an ink containing a first color-changing agent which changes from substantially invisible colorlessness to visibleness by applying a color former. The discoloring area is printed by an ink containing a second color-changing agent which changes a from substantially invisible colorlessness to visibleness by applying the color former and returns to invisible colorlessness state as the time passes naturally after changing its color.</p> |
