Generally, there are the following mathematical symbols: (1) quantitative symbols, such as: I, 2+I, A, X, natural logarithm base E, pi ∏. (2) Operation symbols, such as plus sign (+), minus sign (-), multiplication sign (× or), division (\) and integration (∩). (3) relational symbols: for example, "=" is an equal sign, ""or ""is an approximate symbol, "≦" is an unequal sign, and ">" is a bigger symbol. "