void onepart_filter(int whichpart,double *p,int *ifilter){
  /* This should NOT depend on phi!
     If identical particles, this is only called with whichpart==1,
     If not identical, this gets called with whichpart==1 for the first
     particle and whichpart==2 for the second. */
  *ifilter=1;
}

/* ********************************************* */

void twopart_filter(double *p1,double *p2,int *ifilter){
  *ifilter=1;
}

/* ********************************************* */