reserve X,Y,Z,x,y,z for set;
reserve T,R for Tolerance of X;

theorem
  T c= T*T
proof
  let x,y be object;
  assume
A1: [x,y] in T;
  then y in X by ZFMISC_1:87;
  then [y,y] in T by Th7;
  hence thesis by A1,RELAT_1:def 8;
end;
