thus Sum (digits (3320,10)) = (Sum <%0,2,3%>) + (Sum <%3%>) by Th660, AFINSQ_2:55
.= ((Sum <%0,2%>) + (Sum <%3%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 2) + (Sum <%3%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 2) + 3) + (Sum <%3%>) by AFINSQ_2:53
.= 5 + 3 by AFINSQ_2:53
.= 8 ; :: thesis: verum