thus Sum (digits (3400,10)) = (Sum <%0,0,4%>) + (Sum <%3%>) by Th668, AFINSQ_2:55
.= ((Sum <%0,0%>) + (Sum <%4%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 0) + (Sum <%4%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 0) + 4) + (Sum <%3%>) by AFINSQ_2:53
.= 4 + 3 by AFINSQ_2:53
.= 7 ; :: thesis: verum