thus Sum (digits (4625,10)) = (Sum <%5,2,6%>) + (Sum <%4%>) by Th1347, AFINSQ_2:55
.= ((Sum <%5,2%>) + (Sum <%6%>)) + (Sum <%4%>) by AFINSQ_2:55
.= ((5 + 2) + (Sum <%6%>)) + (Sum <%4%>) by AFINSQ_2:54
.= ((5 + 2) + 6) + (Sum <%4%>) by AFINSQ_2:53
.= 13 + 4 by AFINSQ_2:53
.= 17 ; :: thesis: verum