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

theorem
  TolClasses R c= TolClasses T implies R c= T
proof
  assume
A1: TolClasses R c= TolClasses T;
  let x,y be object;
  assume [x,y] in R;
  then consider Z being TolClass of R such that
A2: x in Z & y in Z by Th20;
  Z in TolClasses R by Def4;
  then Z is TolSet of T by A1,Def4;
  hence thesis by A2,Def1;
end;
