Generally, there are the following mathematical symbols: (1) quantitative symbols: I, 2+I, a, x, natural logarithm base e, pi ∏. (2) Operation symbols: such as plus sign (+), minus sign (-), multiplication sign (× or), division sign (÷ or/), union of two sets (∩), intersection (∩), root sign () and logarithm (log, lg, ln). (3) relational symbols: for example, = is an equal sign, ≈ or ≈ is an approximate symbol, ≠ is an unequal sign, > is a greater than sign,