thus Sum (digits (3680,10)) = (Sum <%0,8,6%>) + (Sum <%3%>) by Th696, AFINSQ_2:55
.= ((Sum <%0,8%>) + (Sum <%6%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 8) + (Sum <%6%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 8) + 6) + (Sum <%3%>) by AFINSQ_2:53
.= 14 + 3 by AFINSQ_2:53
.= 17 ; :: thesis: verum