thus Sum (digits (3600,10)) = (Sum <%0,0,6%>) + (Sum <%3%>) by Th688, AFINSQ_2:55
.= ((Sum <%0,0%>) + (Sum <%6%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 0) + (Sum <%6%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 0) + 6) + (Sum <%3%>) by AFINSQ_2:53
.= 6 + 3 by AFINSQ_2:53
.= 9 ; :: thesis: verum