thus Sum (digits (3500,10)) = (Sum <%0,0,5%>) + (Sum <%3%>) by Th678, AFINSQ_2:55
.= ((Sum <%0,0%>) + (Sum <%5%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 0) + (Sum <%5%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 0) + 5) + (Sum <%3%>) by AFINSQ_2:53
.= 5 + 3 by AFINSQ_2:53
.= 8 ; :: thesis: verum