thus Sum (digits (2160,10)) = (Sum <%0,6,1%>) + (Sum <%2%>) by Th544, AFINSQ_2:55
.= ((Sum <%0,6%>) + (Sum <%1%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 6) + (Sum <%1%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 6) + 1) + (Sum <%2%>) by AFINSQ_2:53
.= 7 + 2 by AFINSQ_2:53
.= 9 ; :: thesis: verum