thus Sum (digits (4450,10)) = (Sum <%0,5,4%>) + (Sum <%4%>) by Th1333, AFINSQ_2:55
.= ((Sum <%0,5%>) + (Sum <%4%>)) + (Sum <%4%>) by AFINSQ_2:55
.= ((0 + 5) + (Sum <%4%>)) + (Sum <%4%>) by AFINSQ_2:54
.= ((0 + 5) + 4) + (Sum <%4%>) by AFINSQ_2:53
.= 9 + 4 by AFINSQ_2:53
.= 13 ; :: thesis: verum