| 摘要 |
Apparatus for educational use, comprising a plurality of pieces and means carrying a regular array of indicia, wherein the pieces are dimensioned and arranged, and the indicia are arrayed, to allow a plurality of said pieces to be juxtaposed adjacent to the indicia, covering a plurality of the indicia, such that each piece covers a single indicium or an integral number of indicia and each indicium covered by a piece is visible through that piece. |
