public static int BinSrch(Comparable a[], int i, int l, Comparable x)
   // Given an array a[i:l] of elements in nondecreasing
   // order, 1<=i<=l, determine whether x is present, and
   // if so, return j such that x == a[j]; else return 0.
   {
      if (l==i) { // If Small(P)
         if (x==a[i]) return i;
         else return 0;
      }
      else { // Reduce P into a smaller subproblem.
         int mid = (i+l)/2;
         if (x == a[mid]) return mid;
         else if (x < a[mid]) return BinSrch(a,i,mid-1,x);
         else return BinSrch(a,mid+1,l,x);
      }
   }