thus Sum (digits (1640,10)) = (Sum <%0,4,6%>) + (Sum <%1%>) by Th492, AFINSQ_2:55
.= ((Sum <%0,4%>) + (Sum <%6%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((0 + 4) + (Sum <%6%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((0 + 4) + 6) + (Sum <%1%>) by AFINSQ_2:53
.= 10 + 1 by AFINSQ_2:53
.= 11 ; :: thesis: verum