thus Sum (digits (888,10)) = (Sum <%8,8%>) + (Sum <%8%>) by Th1072, AFINSQ_2:55
.= (8 + 8) + (Sum <%8%>) by AFINSQ_2:54
.= 16 + 8 by AFINSQ_2:53
.= 24 ; :: thesis: verum