reserve L for non empty doubleLoopStr;
reserve a,b,c,x,y,z for Element of L;
reserve G for left-distributive doubleLoop,
  a,b,x,y for Element of G;

theorem Th7:
  (-b)*a = -(b*a)
proof
  b*a + (-b)*a = (b+(-b))*a by VECTSP_1:def 3
    .= 0.G*a by Def1
    .= 0.G by ALGSTR_1:16;
  hence thesis by Def1;
end;
