theorem Th7:
  compreal is_an_inverseOp_wrt addreal
proof
  let x be Element of REAL;
  thus addreal.(x,compreal.x) = x+compreal.x by BINOP_2:def 9
    .= x+-x by BINOP_2:def 7
    .= the_unity_wrt addreal by BINOP_2:2;
  thus addreal.(compreal.x,x) = compreal.x+x by BINOP_2:def 9
    .= -x+x by BINOP_2:def 7
    .= the_unity_wrt addreal by BINOP_2:2;
end;
