thus Sum (digits (4825,10)) = (Sum <%5,2,8%>) + (Sum <%4%>) by Th1363, AFINSQ_2:55
.= ((Sum <%5,2%>) + (Sum <%8%>)) + (Sum <%4%>) by AFINSQ_2:55
.= ((5 + 2) + (Sum <%8%>)) + (Sum <%4%>) by AFINSQ_2:54
.= ((5 + 2) + 8) + (Sum <%4%>) by AFINSQ_2:53
.= 15 + 4 by AFINSQ_2:53
.= 19 ; :: thesis: verum