thus Sum (digits (2040,10)) = (Sum <%0,4,0%>) + (Sum <%2%>) by Th532, AFINSQ_2:55
.= ((Sum <%0,4%>) + (Sum <%0%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 4) + (Sum <%0%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 4) + 0) + (Sum <%2%>) by AFINSQ_2:53
.= 4 + 2 by AFINSQ_2:53
.= 6 ; :: thesis: verum