thus Sum (digits (1650,10)) = (Sum <%0,5,6%>) + (Sum <%1%>) by Th856, AFINSQ_2:55
.= ((Sum <%0,5%>) + (Sum <%6%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((0 + 5) + (Sum <%6%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((0 + 5) + 6) + (Sum <%1%>) by AFINSQ_2:53
.= 11 + 1 by AFINSQ_2:53
.= 12 ; :: thesis: verum