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  ANSI Common Lisp   12 Numbers   12.2 Dictionary of Numbers

12.2.28 1+, 1- Function

Syntax:
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.

Allegro CL Implementation Details:
None.

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