thus Sum (digits (4875,10)) = (Sum <%5,7,8%>) + (Sum <%4%>) by Th1367, AFINSQ_2:55
.= ((Sum <%5,7%>) + (Sum <%8%>)) + (Sum <%4%>) by AFINSQ_2:55
.= ((5 + 7) + (Sum <%8%>)) + (Sum <%4%>) by AFINSQ_2:54
.= ((5 + 7) + 8) + (Sum <%4%>) by AFINSQ_2:53
.= 20 + 4 by AFINSQ_2:53
.= 24 ; :: thesis: verum