thus Sum (digits (1408,10)) = (Sum <%8,0,4%>) + (Sum <%1%>) by Th836, AFINSQ_2:55
.= ((Sum <%8,0%>) + (Sum <%4%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((8 + 0) + (Sum <%4%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((8 + 0) + 4) + (Sum <%1%>) by AFINSQ_2:53
.= 12 + 1 by AFINSQ_2:53
.= 13 ; :: thesis: verum