thus Sum (digits (4300,10)) = (Sum <%0,0,3%>) + (Sum <%4%>) by Th1321, AFINSQ_2:55
.= ((Sum <%0,0%>) + (Sum <%3%>)) + (Sum <%4%>) by AFINSQ_2:55
.= ((0 + 0) + (Sum <%3%>)) + (Sum <%4%>) by AFINSQ_2:54
.= ((0 + 0) + 3) + (Sum <%4%>) by AFINSQ_2:53
.= 3 + 4 by AFINSQ_2:53
.= 7 ; :: thesis: verum