/* Binary search interface
 * 15-122 Principle of Imperative Computation, Spring 2010
 * Frank Pfenning
 */

bool is_sorted(int[] A, int n)
//@requires 0 <= n && n <= \length(A);
;

bool is_in(int x, int[] A, int n)
//@requires 0 <= n && n <= \length(A);
;

int binsearch(int x, int[] A, int n)
//@requires 0 <= n && n <= \length(A);
//@requires is_sorted(A, n);
/*@ensures (-1 == \result && !is_in(x, A, n))
        || ((0 <= \result && \result < n) && A[\result] == x);
  @*/
;