thus Sum (digits (1104,10)) = (Sum <%4,0,1%>) + (Sum <%1%>) by Th999, AFINSQ_2:55
.= ((Sum <%4,0%>) + (Sum <%1%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((4 + 0) + (Sum <%1%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((4 + 0) + 1) + (Sum <%1%>) by AFINSQ_2:53
.= 5 + 1 by AFINSQ_2:53
.= 6 ; :: thesis: verum