thus Sum (digits (2060,10)) = (Sum <%0,6,0%>) + (Sum <%2%>) by Th534, AFINSQ_2:55
.= ((Sum <%0,6%>) + (Sum <%0%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 6) + (Sum <%0%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 6) + 0) + (Sum <%2%>) by AFINSQ_2:53
.= 6 + 2 by AFINSQ_2:53
.= 8 ; :: thesis: verum