thus Sum (digits (3480,10)) = (Sum <%0,8,4%>) + (Sum <%3%>) by Th676, AFINSQ_2:55
.= ((Sum <%0,8%>) + (Sum <%4%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 8) + (Sum <%4%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 8) + 4) + (Sum <%3%>) by AFINSQ_2:53
.= 12 + 3 by AFINSQ_2:53
.= 15 ; :: thesis: verum