i := hashfunction( key ) mod md;
     read-directory-entry( i ) into npage;
     read-leaf-page( npage ) into r;
     i := 1;
     while (i<b) and (r[i].k <> key) do i := i+1;
     if r[i].k = key then     found( r[i] )
          else      notfound( key );