thus Sum (digits (2068,10)) = (Sum <%8,6,0%>) + (Sum <%2%>) by Th890, AFINSQ_2:55
.= ((Sum <%8,6%>) + (Sum <%0%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((8 + 6) + (Sum <%0%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((8 + 6) + 0) + (Sum <%2%>) by AFINSQ_2:53
.= 14 + 2 by AFINSQ_2:53
.= 16 ; :: thesis: verum