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#### C.4.3 A `lambda` Expression: Useful Anonymity

`lambda` is the symbol for an anonymous function, a function without a name. Every time you use an anonymous function, you need to include its whole body.

Thus,

```(lambda (arg) (/ arg 50))
```

is a function definition that says ‘return the value resulting from dividing whatever is passed to me as `arg` by 50’.

Earlier, for example, we had a function `multiply-by-seven`; it multiplied its argument by 7. This function is similar, except it divides its argument by 50; and, it has no name. The anonymous equivalent of `multiply-by-seven` is:

```(lambda (number) (* 7 number))
```

If we want to multiply 3 by 7, we can write:

```(multiply-by-seven 3)
\_______________/ ^
|         |
function  argument
```

This expression returns 21.

Similarly, we can write:

```((lambda (number) (* 7 number)) 3)
\____________________________/ ^
|                |
anonymous function     argument
```

If we want to divide 100 by 50, we can write:

```((lambda (arg) (/ arg 50)) 100)
\______________________/  \_/
|              |
anonymous function   argument
```

This expression returns 2. The 100 is passed to the function, which divides that number by 50.

See Lambda Expressions in The GNU Emacs Lisp Reference Manual, for more about `lambda`. Lisp and lambda expressions derive from the Lambda Calculus.