\datethis
@* Intro. Pepperdine's method for topswops. [Reference: {\sl Mathematical
Gazette\/ \bf73} (1989), 131--133.]

@d n 15 /* degree of perms; should be less than 16 */
@d maxl 1000 /* max level */

@c
#include <stdio.h>
typedef struct {char p[16];} perm; /* this speeds it up by better than 2 */
perm a[maxl];
perm b[maxl];
char x[maxl];

main()
{
  register int j,k,l,m;
  a[0].p[0]=1;
  m=l=0;
 tryit: k=++x[l];
  if (k<n) {
    if (a[l].p[k]==0) {
      if (b[l].p[k+1]!=0) goto tryit;
    }@+else if (a[l].p[k]!=k+1) goto tryit;
    a[l+1]=a[l];
    for (j=1;j<=k;j++) a[l+1].p[j]=a[l].p[k-j];
    b[l+1]=b[l];
    a[l+1].p[0]=k+1, b[l+1].p[k+1]=1;
    if (l>=m) {
      m=l;
      printf("%d:",m+1);
      for (j=0;j<n;j++) printf(" %d",a[l+1].p[j]);
      printf("\n");
    }
    l++; x[l]=0;
    goto tryit;
  }
  l--;
  if (l>=0) goto tryit;
}

@*Index.