thus Sum (digits (1056,10)) = (Sum <%6,5,0%>) + (Sum <%1%>) by Th808, AFINSQ_2:55
.= ((Sum <%6,5%>) + (Sum <%0%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((6 + 5) + (Sum <%0%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((6 + 5) + 0) + (Sum <%1%>) by AFINSQ_2:53
.= 11 + 1 by AFINSQ_2:53
.= 12 ; :: thesis: verum