given a set with the symbols :

" + " for addition

" - " for inverse

the constants :

0

AND the axioms:

for all a,b,c : a+(b+c) = (a+b) + c

for all a : a+0 = a

for all a : a +(-a) =0

for all a,b : a+b = b+a

PROVE using CONTRADICTION

1) THE uniqness of zero

2) THE uniqness of the inverse