thus Sum (digits (2180,10)) = (Sum <%0,8,1%>) + (Sum <%2%>) by Th546, AFINSQ_2:55
.= ((Sum <%0,8%>) + (Sum <%1%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 8) + (Sum <%1%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 8) + 1) + (Sum <%2%>) by AFINSQ_2:53
.= 9 + 2 by AFINSQ_2:53
.= 11 ; :: thesis: verum