thus Sum (digits (3520,10)) = (Sum <%0,2,5%>) + (Sum <%3%>) by Th680, AFINSQ_2:55
.= ((Sum <%0,2%>) + (Sum <%5%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 2) + (Sum <%5%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 2) + 5) + (Sum <%3%>) by AFINSQ_2:53
.= 7 + 3 by AFINSQ_2:53
.= 10 ; :: thesis: verum