thus Sum (digits (1035,10)) = (Sum <%5,3,0%>) + (Sum <%1%>) by Th993, AFINSQ_2:55
.= ((Sum <%5,3%>) + (Sum <%0%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((5 + 3) + (Sum <%0%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((5 + 3) + 0) + (Sum <%1%>) by AFINSQ_2:53
.= 8 + 1 by AFINSQ_2:53
.= 9 ; :: thesis: verum