thus Sum (digits (1081,10)) = (Sum <%1,8,0%>) + (Sum <%1%>) by Th997, AFINSQ_2:55
.= ((Sum <%1,8%>) + (Sum <%0%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((1 + 8) + (Sum <%0%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((1 + 8) + 0) + (Sum <%1%>) by AFINSQ_2:53
.= 9 + 1 by AFINSQ_2:53
.= 10 ; :: thesis: verum