Paper corner label. Refers to the number in the upper right corner when citing references in paper writing. There are more than one reference cited in the paper, and the source must be indicated. First, you need a corner marker. Direct quotation refers to the original text of authoritative works, with colons and quotation marks. After the quotation is finished, mark the serial number with parentheses in the upper right corner of the back quotation mark. After writing the paper, write the reference sources by serial number.