theorem Th50:
  compcomplex is_an_inverseOp_wrt addcomplex
proof
  let c;
  thus addcomplex.(c,compcomplex.c) = c+compcomplex.c by BINOP_2:def 3
    .= c+-c by BINOP_2:def 1
    .= the_unity_wrt addcomplex by BINOP_2:1;
  thus addcomplex.(compcomplex.c,c) = compcomplex.c+c by BINOP_2:def 3
    .= -c+c by BINOP_2:def 1
    .= the_unity_wrt addcomplex by BINOP_2:1;
end;
