thus Sum (digits (3360,10)) = (Sum <%0,6,3%>) + (Sum <%3%>) by Th664, AFINSQ_2:55
.= ((Sum <%0,6%>) + (Sum <%3%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 6) + (Sum <%3%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 6) + 3) + (Sum <%3%>) by AFINSQ_2:53
.= 9 + 3 by AFINSQ_2:53
.= 12 ; :: thesis: verum