thus Sum (digits (350,10)) = (Sum <%0,5%>) + (Sum <%3%>) by Th1089, AFINSQ_2:55
.= (0 + 5) + (Sum <%3%>) by AFINSQ_2:54
.= 5 + 3 by AFINSQ_2:53
.= 8 ; :: thesis: verum