reserve W,X,Y,Z for set,
  f,g for Function,
  a,x,y,z for set;
reserve u,v for Element of Tarski-Class(X),
  A,B,C for Ordinal,
  L for Sequence;

theorem Th44:
  x in Rank A & y in Rank A iff {x,y} in Rank succ A
proof
 x in Rank A & y in Rank A iff {x,y} c= Rank A by ZFMISC_1:32;
  hence thesis by Th32;
end;
