def unknown_pairs_present(grm,sites_cart,site_labels):
  """
  Test if PDB file contains unknown type pairs

  Args:
    grm (obj): geometry restraints manager
    sites_cart (flex.vec3): atoms sites cart (coordinates)
    site_labels: a list of lables such as " HA  LEU A  38 ", for each atom

  Return:
    (bool): True if PDB file contains unknown type pairs
  """
  pp= grm.pair_proxies(sites_cart=sites_cart,site_labels=site_labels)
  return (pp.nonbonded_proxies.n_unknown_nonbonded_type_pairs != 0)