"△" represents an operation symbol, its meaning is: a△b=2a-b, if x△(2△3)=3, then: x=how much.
"△"表示一种运算符号，其意义是：a△b=2a-b，如果x△(2△3)=3，则：x=多少．
<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">4 - 3</gadget>
<output>1</output>

<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<result>2</result>