thus Sum (digits (2575,10)) = (Sum <%5,7,5%>) + (Sum <%2%>) by Th1211, AFINSQ_2:55
.= ((Sum <%5,7%>) + (Sum <%5%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((5 + 7) + (Sum <%5%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((5 + 7) + 5) + (Sum <%2%>) by AFINSQ_2:53
.= 17 + 2 by AFINSQ_2:53
.= 19 ; :: thesis: verum