A question about the topallhdg.pro of xplorv3851

[Min Zhang]

Would someone please explain the term "ic" in the file topallhdg.pro,
which is new in v3851 ?

e.g: 

residue ALA
  group
    atom N   type=NH1 charge=-0.36 end
    atom HN  type=H   charge= 0.26 end
    atom CA  type=CT  charge= 0.00 end
    atom HA  type=HA  charge= 0.10 end
    atom CB  type=CT  charge=-0.30 end
    atom HB1 type=HA  charge= 0.10 end
    atom HB2 type=HA  charge= 0.10 end
    atom HB3 type=HA  charge= 0.10 end
    atom C   type=C   charge= 0.48 end
    atom O   type=O   charge=-0.48 end

  bond N  HN       
  bond N  CA    bond CA  HA   
  bond CA  CB   bond CB  HB1   bond CB  HB2     bond CB  HB3
  bond CA  C       
  bond C   O

  improper HA  N   C   CB  !stereo CA
  improper HB1 HB2 CA HB3  !stereo CB

  ic N C *CA CB  0.0 0.0  120.0  0.0 0.0
end
 
Thanks,


Min Zhang