thus Sum (digits (3325,10)) = (Sum <%5,2,3%>) + (Sum <%3%>) by Th1255, AFINSQ_2:55
.= ((Sum <%5,2%>) + (Sum <%3%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((5 + 2) + (Sum <%3%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((5 + 2) + 3) + (Sum <%3%>) by AFINSQ_2:53
.= 10 + 3 by AFINSQ_2:53
.= 13 ; :: thesis: verum