thus Sum (digits (2525,10)) = (Sum <%5,2,5%>) + (Sum <%2%>) by Th1207, AFINSQ_2:55
.= ((Sum <%5,2%>) + (Sum <%5%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((5 + 2) + (Sum <%5%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((5 + 2) + 5) + (Sum <%2%>) by AFINSQ_2:53
.= 12 + 2 by AFINSQ_2:53
.= 14 ; :: thesis: verum