lispdoc - results for 1- 

minus
 
 Mentioned in:
HyperSpec - 2.4.8.18 Sharpsign Minus
(1- number)
Function: Return NUMBER - 1.
Example:
(defun yesterday (parsed-values)
  (set-current-value parsed-values :date t :zone
   t)
  (setf (decoded-time-day parsed-values)
          (1- (decoded-time-day parsed-values))))
Mentioned in:
CLtL2 - 12.4. Arithmetic Operations
HyperSpec - Function 1+, 1-
On Lisp - Anaphoric Variants
On Lisp - Conditional Evaluation
On Lisp - Functional Design
On Lisp - Non-functional Expanders
PCL - basic math

By Bill Moorier