thus Sum (digits (2700,10)) = (Sum <%0,0,7%>) + (Sum <%2%>) by Th598, AFINSQ_2:55
.= ((Sum <%0,0%>) + (Sum <%7%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 0) + (Sum <%7%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 0) + 7) + (Sum <%2%>) by AFINSQ_2:53
.= 7 + 2 by AFINSQ_2:53
.= 9 ; :: thesis: verum