#### 12.2.28 1+, 1- [Function]

`1` + ⇒ number successor `1` - ⇒ number predecessor

#### Arguments and Values::

number—a number.

successor, predecessor—a number.

#### Description::

1+ returns a number that is one more than its argument number. 1- returns a number that is one less than its argument number.

#### Examples::

     (1+ 99) ⇒  100
     (1- 100) ⇒  99
     (1+ (complex 0.0)) ⇒  #C(1.0 0.0)
     (1- 5/3) ⇒  2/3

#### Exceptional Situations::

Might signal type-error if its argument is not a number. Might signal arithmetic-error.

#### See Also::

incf , decf

#### Notes::

     (1+ number) ≡ (+ number 1)
     (1- number) ≡ (- number 1)

Implementors are encouraged to make the performance of both the previous expressions be the same.