thus Sum (digits (3425,10)) = (Sum <%5,2,4%>) + (Sum <%3%>) by Th1261, AFINSQ_2:55
.= ((Sum <%5,2%>) + (Sum <%4%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((5 + 2) + (Sum <%4%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((5 + 2) + 4) + (Sum <%3%>) by AFINSQ_2:53
.= 11 + 3 by AFINSQ_2:53
.= 14 ; :: thesis: verum