let L be non empty addLoopStr ; :: thesis: ( L is AddGroup iff ( ( for a being Element of L holds a + (0. L) = a ) & ( for a being Element of L ex x being Element of L st a + x = 0. L ) & ( for a, b, c being Element of L holds (a + b) + c = a + (b + c) ) ) )
thus ( L is AddGroup implies ( ( for a being Element of L holds a + (0. L) = a ) & ( for a being Element of L ex x being Element of L st a + x = 0. L ) & ( for a, b, c being Element of L holds (a + b) + c = a + (b + c) ) ) ) by ; :: thesis: ( ( for a being Element of L holds a + (0. L) = a ) & ( for a being Element of L ex x being Element of L st a + x = 0. L ) & ( for a, b, c being Element of L holds (a + b) + c = a + (b + c) ) implies L is AddGroup )
assume that
A1: for a being Element of L holds a + (0. L) = a and
A2: for a being Element of L ex x being Element of L st a + x = 0. L and
A3: for a, b, c being Element of L holds (a + b) + c = a + (b + c) ; :: thesis: L is AddGroup
L is right_complementable
proof
let a be Element of L; :: according to ALGSTR_0:def 16 :: thesis:
thus ex x being Element of L st a + x = 0. L by A2; :: according to ALGSTR_0:def 11 :: thesis: verum
end;
hence L is AddGroup by ; :: thesis: verum