thus Sum (digits (2800,10)) = (Sum <%0,0,8%>) + (Sum <%2%>) by Th608, AFINSQ_2:55
.= ((Sum <%0,0%>) + (Sum <%8%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 0) + (Sum <%8%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 0) + 8) + (Sum <%2%>) by AFINSQ_2:53
.= 8 + 2 by AFINSQ_2:53
.= 10 ; :: thesis: verum