thus Sum (digits (2000,10)) = (Sum <%0,0,0%>) + (Sum <%2%>) by Th528, AFINSQ_2:55
.= ((Sum <%0,0%>) + (Sum <%0%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 0) + (Sum <%0%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 0) + 0) + (Sum <%2%>) by AFINSQ_2:53
.= 2 by AFINSQ_2:53 ; :: thesis: verum