thus Sum (digits (3275,10)) = (Sum <%5,7,2%>) + (Sum <%3%>) by Th1253, AFINSQ_2:55
.= ((Sum <%5,7%>) + (Sum <%2%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((5 + 7) + (Sum <%2%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((5 + 7) + 2) + (Sum <%3%>) by AFINSQ_2:53
.= 14 + 3 by AFINSQ_2:53
.= 17 ; :: thesis: verum