reserve f,g,h for Function,
  A for set;

theorem Th1:
  delta A = <:id A, id A:>
proof
  thus delta A = id [:A,A:]*delta A by FUNCT_2:17
    .= [:id A, id A:]*delta A by FUNCT_3:69
    .= <:id A, id A:> by FUNCT_3:78;
end;
