thus Sum (digits (1840,10)) = (Sum <%0,4,8%>) + (Sum <%1%>) by Th512, AFINSQ_2:55
.= ((Sum <%0,4%>) + (Sum <%8%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((0 + 4) + (Sum <%8%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((0 + 4) + 8) + (Sum <%1%>) by AFINSQ_2:53
.= 12 + 1 by AFINSQ_2:53
.= 13 ; :: thesis: verum