thus Sum (digits (3060,10)) = (Sum <%0,6,0%>) + (Sum <%3%>) by Th634, AFINSQ_2:55
.= ((Sum <%0,6%>) + (Sum <%0%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 6) + (Sum <%0%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 6) + 0) + (Sum <%3%>) by AFINSQ_2:53
.= 6 + 3 by AFINSQ_2:53
.= 9 ; :: thesis: verum