
theorem GROUP630:
  for G being strict Group, N be strict normal Subgroup of G
  st G is commutative
  holds G./.N is commutative
  proof
    let G be strict Group, N be strict normal Subgroup of G;
    assume G is commutative;
    then G` = (1).G by GROUP_5:75;
    then G` = (1).N by GROUP_2:63;
    hence thesis by GROUP_6:30;
  end;
