thus Sum (digits (725,10)) = (Sum <%5,2%>) + (Sum <%7%>) by Th1103, AFINSQ_2:55
.= (5 + 2) + (Sum <%7%>) by AFINSQ_2:54
.= 7 + 7 by AFINSQ_2:53
.= 14 ; :: thesis: verum