thus Sum (digits (1610,10)) = (Sum <%0,1,6%>) + (Sum <%1%>) by Th1039, AFINSQ_2:55
.= ((Sum <%0,1%>) + (Sum <%6%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((0 + 1) + (Sum <%6%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((0 + 1) + 6) + (Sum <%1%>) by AFINSQ_2:53
.= 7 + 1 by AFINSQ_2:53
.= 8 ; :: thesis: verum