sub add_son_father_pair {
  # show the "before" data
  print "add_son_father_pair before\n";
  output_hash_neatly();

  my $name1 = ask_question("Enter a male name: ");
  if (exists $son_father{$name1}) {
     print "Duplicate name -- try again!\n";
     return;
  }

  my $add_dad = ask_question("Add a father: ");
  $son_father{$name1} = $add_dad;

  # Did we do it right?
  print "add_son_father_pair after:\n";
  output_hash_neatly();
}