// output of ./demo/comb/perm-involution-demo.cc:
// Description:
//% Generate all involutions (self-inverse permutations).

arg 1: 5 == n  [Self-inverse permutations of n elements (n>=1).]  default=5
   0:  [ . 1 2 3 4 ]    (0) (1) (2) (3) (4) 
   1:  [ . 1 2 4 3 ]    (0) (1) (2) (3, 4)  
   2:  [ . 1 4 3 2 ]    (0) (1) (2, 4) (3)  
   3:  [ . 4 2 3 1 ]    (0) (1, 4) (2) (3)  
   4:  [ 4 1 2 3 . ]    (0, 4) (1) (2) (3)  
   5:  [ . 1 3 2 4 ]    (0) (1) (2, 3) (4)  
   6:  [ . 4 3 2 1 ]    (0) (1, 4) (2, 3)   
   7:  [ 4 1 3 2 . ]    (0, 4) (1) (2, 3)   
   8:  [ . 3 2 1 4 ]    (0) (1, 3) (2) (4)  
   9:  [ . 3 4 1 2 ]    (0) (1, 3) (2, 4)   
  10:  [ 4 3 2 1 . ]    (0, 4) (1, 3) (2)   
  11:  [ 3 1 2 . 4 ]    (0, 3) (1) (2) (4)  
  12:  [ 3 1 4 . 2 ]    (0, 3) (1) (2, 4)   
  13:  [ 3 4 2 . 1 ]    (0, 3) (1, 4) (2)   
  14:  [ . 2 1 3 4 ]    (0) (1, 2) (3) (4)  
  15:  [ . 2 1 4 3 ]    (0) (1, 2) (3, 4)   
  16:  [ 4 2 1 3 . ]    (0, 4) (1, 2) (3)   
  17:  [ 3 2 1 . 4 ]    (0, 3) (1, 2) (4)   
  18:  [ 2 1 . 3 4 ]    (0, 2) (1) (3) (4)  
  19:  [ 2 1 . 4 3 ]    (0, 2) (1) (3, 4)   
  20:  [ 2 4 . 3 1 ]    (0, 2) (1, 4) (3)   
  21:  [ 2 3 . 1 4 ]    (0, 2) (1, 3) (4)   
  22:  [ 1 . 2 3 4 ]    (0, 1) (2) (3) (4)  
  23:  [ 1 . 2 4 3 ]    (0, 1) (2) (3, 4)   
  24:  [ 1 . 4 3 2 ]    (0, 1) (2, 4) (3)   
  25:  [ 1 . 3 2 4 ]    (0, 1) (2, 3) (4)   
 ct=26