Is it a typo?

[xxx]

Hi,

Thank Mr. Ursby for his kindly advice for my sigmaa weghting map problem.
I get good fo-fc map now. This mailing list is so helpful that I can 
always get answers from some experienced crystallographer. I love this 
mailing list.

Now I have another question to ask. I noticed that in
toppar/protein_rep.param file there are some lines as following: 

--------------------------------
{* nonbonding parameter section *}
!  This uses a new form of the REPEL function:
!    fVDW(R) =  RCON *( Rmin ^ IREX - R  ^ IREX ) ^ REXP
!
!  PROLSQ uses a function of the form:
!    fVDW(R) =  (1 / 0.5) ^ 4 * ( Rmin ^ 4 - R  ^ 4 ) 
!
!  The epsilon values are arbitrary since the repel function does not 
!depend on epsilon.  The sigma values come from converting the Van der Waals 
!   radii of the PROLSQ program into sigma values using the formula:
!     Rmin = sigma * 2 ^ (1/6)

...

 NBONds
  CUTNB=7.0   WMIN=1.5
  REPEl = 1.0 
  REXPonent = 4
  IREXponent = 1
  RCONst = 16.0
  TOLErance = 0.5      NBXMOD = 5
  ctonnb=5.5 ctofnb=6.0 {* for consistency only, not needed for repel *}
END
--------------------------------------------

Note the REXPonent and IREXponent values. It means that the REPEL 
function is :
    fVDW(R) =  16.0 * (Rmin^1 - R^1)^4
Obviously this is not consistent with the PROLSQ's function.

Is this a typo?

Thank you in advance.

Xiaozhou.
-------------------------------------------------------
  Xiaozhou Liu
  Biophysics and Physiology Department
  College of Life Science
  Peking University
  Beijing 100871, P.R.China
                                             
  E-mail: liuxz at iris.lsc.pku.edu.cn
          liuxz at pubms.pku.edu.cn
  Telephone: +86 10 62751864
-------------------------------------------------------