
theorem Th34:
for X being set, x, y being set st x in X & y in X
  holds {x,y} in CompleteSGraph X
proof
  let X be set, x,y be set such that
A1: x in X and
A2: y in X;
A3: {x, y} c= X by A1,A2,ZFMISC_1:32;
A4: card {x,y} <= 2 by CARD_2:50;
  thus {x,y} in CompleteSGraph X by A4,A3;
end;
