thus Sum (digits (2320,10)) = (Sum <%0,2,3%>) + (Sum <%2%>) by Th560, AFINSQ_2:55
.= ((Sum <%0,2%>) + (Sum <%3%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 2) + (Sum <%3%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 2) + 3) + (Sum <%2%>) by AFINSQ_2:53
.= 5 + 2 by AFINSQ_2:53
.= 7 ; :: thesis: verum