thus Sum (digits (1450,10)) = (Sum <%0,5,4%>) + (Sum <%1%>) by Th1145, AFINSQ_2:55
.= ((Sum <%0,5%>) + (Sum <%4%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((0 + 5) + (Sum <%4%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((0 + 5) + 4) + (Sum <%1%>) by AFINSQ_2:53
.= 9 + 1 by AFINSQ_2:53
.= 10 ; :: thesis: verum