thus Sum (digits (3640,10)) = (Sum <%0,4,6%>) + (Sum <%3%>) by Th692, AFINSQ_2:55
.= ((Sum <%0,4%>) + (Sum <%6%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 4) + (Sum <%6%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 4) + 6) + (Sum <%3%>) by AFINSQ_2:53
.= 10 + 3 by AFINSQ_2:53
.= 13 ; :: thesis: verum