thus Sum (digits (2825,10)) = (Sum <%5,2,8%>) + (Sum <%2%>) by Th1225, AFINSQ_2:55
.= ((Sum <%5,2%>) + (Sum <%8%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((5 + 2) + (Sum <%8%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((5 + 2) + 8) + (Sum <%2%>) by AFINSQ_2:53
.= 15 + 2 by AFINSQ_2:53
.= 17 ; :: thesis: verum