thus Sum (digits (1340,10)) = (Sum <%0,4,3%>) + (Sum <%1%>) by Th462, AFINSQ_2:55
.= ((Sum <%0,4%>) + (Sum <%3%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((0 + 4) + (Sum <%3%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((0 + 4) + 3) + (Sum <%1%>) by AFINSQ_2:53
.= 7 + 1 by AFINSQ_2:53
.= 8 ; :: thesis: verum