thus Sum (digits (2640,10)) = (Sum <%0,4,6%>) + (Sum <%2%>) by Th592, AFINSQ_2:55
.= ((Sum <%0,4%>) + (Sum <%6%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 4) + (Sum <%6%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 4) + 6) + (Sum <%2%>) by AFINSQ_2:53
.= 10 + 2 by AFINSQ_2:53
.= 12 ; :: thesis: verum