Text ( visual ) : unmediated Words in color / [by Caleb Gattegno]. -- Completely rev. ed. -- : R1 ; : R2 ; : R3. -- New York : Educational Solutions , c1977. -- v. ; 19 cm. -- ISBN 0878251286 ; 0878251294 ; 0878251308 ; (BA69943446) ; https://ci.nii.ac.jp/ncid/BA69943446 Author Heading(s): Gattegno, Caleb