thus Sum (digits (275,10)) = (Sum <%5,7%>) + (Sum <%2%>) by Th1085, AFINSQ_2:55
.= (5 + 7) + (Sum <%2%>) by AFINSQ_2:54
.= 12 + 2 by AFINSQ_2:53
.= 14 ; :: thesis: verum