thus Sum (digits (2310,10)) = (Sum <%0,1,3%>) + (Sum <%2%>) by Th910, AFINSQ_2:55
.= ((Sum <%0,1%>) + (Sum <%3%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 1) + (Sum <%3%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 1) + 3) + (Sum <%2%>) by AFINSQ_2:53
.= 4 + 2 by AFINSQ_2:53
.= 6 ; :: thesis: verum