thus Sum (digits (4325,10)) = (Sum <%5,2,3%>) + (Sum <%4%>) by Th1323, AFINSQ_2:55
.= ((Sum <%5,2%>) + (Sum <%3%>)) + (Sum <%4%>) by AFINSQ_2:55
.= ((5 + 2) + (Sum <%3%>)) + (Sum <%4%>) by AFINSQ_2:54
.= ((5 + 2) + 3) + (Sum <%4%>) by AFINSQ_2:53
.= 10 + 4 by AFINSQ_2:53
.= 14 ; :: thesis: verum