User's Manual

140
You may charge a fee for the physical act of transferring a
copy, and you may at your option offer warranty protection in
exchange for a fee.
2. You may modify your copy or copies of the Program or any
portion of it, thus forming a work based on the Program, and
copy and distribute such modifications or work under the
terms of Section 1 above, provided that you also meet all of
these conditions:
a) You must cause the modified files to carry prominent
notices stating that you changed the files and the date of any
change.
b) You must cause any work that you distribute or publish, that
in whole or in part contains or is derived from the Program or
any part thereof, to be licensed as a whole at no charge to all
third parties under the terms of this License.
c) If the modified program normally reads commands
interactively when run, you must cause it, when started
running for such interactive use in the most ordinary way, to
print or display an announcement including an appropriate
copyright notice and a notice that there is no warranty (or
else, saying that you provide a warranty) and that users may
redistribute the program under these conditions, and telling
the user how to view a copy of this License. (Exception: if the
Program itself is interactive but does not normally print such
an announcement, your work based on the Program is not
required to print an announcement.)