DETAILED DESCRIPTION I claim: 1.
A reusable hidden indicia printed sheet comprising a paper containing a first color-forming area printed thereon by using an ink containing a first color-changing agent which changes from substantially invisible colorlessness to visibleness by applying a color former, wherein said color former comprises a solution pH indicator and a second color-forming area printed upon the paper separate from said first color-forming area by using an ink containing a second color-changing agent which changes from substantially invisible colorlessness to visibleness by applying said color former and fades to a colorless state quickly whereas said first color-forming area fades to a colorless state slowly.
2.
The reusable hidden indicia printed sheet of claim 1, further including a pH regulating agent.
3.
The print of claim 2, wherein the pH regulating agent is present in the ink.
4.
The print of claim 2, wherein the pH regulating agent is present in the color former.
5.
A reusable hidden indicia printed sheet according to claim 1, wherein said pH indicator is selected from the group consisting of .
gamma.
-dinitrophenol, m-nitrophenol, o-nitrophenol, p-nitrophenol, cyanine, .
alpha.
-naphtholphthalein, phenolphthalein, cresolphthalein, thymolphthalein, ethylbis-acetic acid, bromphenol purple, hexamethoxy red, heptamethoxy red and mixtures thereof.
6.
A print according to claim 2, wherein said pH regulator is selected from the group consisting of ammonia, monoethanolamine, 3-ethoxypropylamine, diisobutylamine, secbutylamine, isopropanolamine, ethanolamine, 2-ethylhexylamine, ethyleneamine, acetic acid and formic acid.
Description:
The present invention relates to a print which allows an effective education in repetition and can improve educational efficiency by comprising a color-forming area printed by using an ink which changes to a visible color by applying a color former and a discoloring area which changes to colorlessness after changing color by aforementioned means
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Quantum Computing 
