thus Sum (digits (4150,10)) = (Sum <%0,5,1%>) + (Sum <%4%>) by Th1309, AFINSQ_2:55
.= ((Sum <%0,5%>) + (Sum <%1%>)) + (Sum <%4%>) by AFINSQ_2:55
.= ((0 + 5) + (Sum <%1%>)) + (Sum <%4%>) by AFINSQ_2:54
.= ((0 + 5) + 1) + (Sum <%4%>) by AFINSQ_2:53
.= 6 + 4 by AFINSQ_2:53
.= 10 ; :: thesis: verum