5 12 70
  This menu item allows the user to define the momentum distribution 
function (PDF) for the first and second incoming particles. 
The name of the activated distribution is displayed in the corresponding 
menu. "Momentum distribution OFF" selection  means that the 
convolution of the matrix element squared with a distribution function
will be not performed.
  The user can display a plot for the distribution by pressing 
the F7 key.
