在所引的例题中给代数式中的字母不是一个数值,而是几个数值.这就引导学生惯于把代数式看作它的字母的函数(而不仅是对象的恆等变换).在复习所讲过的教材时,练习题可以这样选择,使它给出来的任意值不是一个字母而是两个或几个字母.扩充练习的题目也是有用的.像在学年终了时,可以向学生提出, In the example cited, the letters in algebraic expressions are not a single number, but several values. This leads students to use algebraic expression as a function of their letters (not just the identity of the object). When speaking about a textbook, practice questions can be chosen so that any given value is not a letter but two or more letters. The topic of an extended exercise is also useful. As at the end of the school year, students can ask questions.