For example, subtracting −5 from 3 might be read as "positive three take away negative 5" and be shown as  or even as  In grading systems (such as examination marks), the plus sign indicates a grade one level higher and the minus sign a grade lower. For example, ("B minus") is one grade lower than . Sometimes this is extended to two plus or minus signs; for example is two grades higher than . Positive and negative are sometimes abbreviated as and . In mathematics the one-sided limit means approaches from the right, and means approaches from the left. For example, as but as . Blood types are often qualified with a plus or minus to indicate the presence or absence of the Rh factor; for instance, A+ means A-type blood with the Rh factor present, while B− means B-type blood with the Rh factor absent. In music, augmented chords are symbolized with a plus sign, although this practice is not universal as there are other methods for spelling those chords. For example, "C+" is read "C augmented chord". Also used as superscript. As well as the normal mathematical usage, plus and minus signs may be used for a number of other purposes in computing. Plus and minus signs are often used in tree view on a computer screen to show if a folder is collapsed or not. In some programming languages, concatenation of strings is written , and results in . In most programming languages, subtraction and negation are indicated with the ASCII hyphen-minus character, . In APL a raised minus sign (Unicode U+00AF) is used to denote a negative number, as in . While in J a negative number is denoted by an underscore, as in . In C and some other computer programming languages, two plus signs indicate the increment operator and two minus signs a decrement; the position of the operator before or after the variable indicates whether the new or old value is read from it. For example, if x equals 6, then increments x to 7 but sets y to 6, whereas would set both x and y to 7. By extension, is sometimes used in computing terminology to signify an improvement, as in the name of the language C++. In regular expressions, "+" is often used to indicate "1 or more" in a pattern to be matched. For example, "x+" means "one or more of the letter x". There is no concept of negative zero in mathematics, but in computing −0 may have a separate representation from zero.