thus Sum (digits (3825,10)) = (Sum <%5,2,8%>) + (Sum <%3%>) by Th1285, AFINSQ_2:55
.= ((Sum <%5,2%>) + (Sum <%8%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((5 + 2) + (Sum <%8%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((5 + 2) + 8) + (Sum <%3%>) by AFINSQ_2:53
.= 15 + 3 by AFINSQ_2:53
.= 18 ; :: thesis: verum