reserve X,Y,Z for set,
  a,b,c,d,x,y,z,u for object,
  R for Relation,
  A,B,C for Ordinal;
reserve H for Function;

theorem Th5:
  R,RelIncl A are_isomorphic & R,RelIncl B are_isomorphic implies A = B
proof
  assume that
A1: R,RelIncl A are_isomorphic and
A2: R,RelIncl B are_isomorphic;
  RelIncl A,R are_isomorphic by A1,WELLORD1:40;
  hence thesis by A2,Th4,WELLORD1:42;
end;
