theorem Th60:
for R being add-associative right_zeroed right_complementable
            non empty doubleLoopStr,
    a being Element of R holds (-1) '*' a = -a
proof
let R be add-associative right_zeroed right_complementable
         non empty doubleLoopStr,
    a being Element of R;
(-1) '*' a = - (1*a) by Def2 .= - a by BINOM:13;
hence thesis;
end;
