"""
Show explicitly that de Morgan's Laws are correct.
Oct 14 homework sol'n by Jim M.

See http://en.wikipedia.org/wiki/De_Morgan_duality

"""

print "truth tables for de Morgan's Laws"
print

morgans_laws  = [ ["not (P and Q)", "(not P) or  (not Q)"],
                  ["not (P or Q)",  "(not P) and (not Q)"]  ]

format = " %8s  %8s  %20s  %20s    %6s "

for statements in morgans_laws:
  left_string  = statements[0]
  right_string = statements[1]
  print format % ('P', 'Q', left_string, right_string, 'same')
  print format % ('-'*8, '-'*8, '-'*20, '-'*20, '-'*6)
  for P in (True, False):
    for Q in (True, False):
      left  = eval(left_string)
      right = eval(right_string)
      if left == right:
        same = 'yes'
      else:
        same = 'no'
      print format % (P, Q, left, right, same)
  print