thus Sum (digits (3840,10)) = (Sum <%0,4,8%>) + (Sum <%3%>) by Th712, AFINSQ_2:55
.= ((Sum <%0,4%>) + (Sum <%8%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 4) + (Sum <%8%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 4) + 8) + (Sum <%3%>) by AFINSQ_2:53
.= 12 + 3 by AFINSQ_2:53
.= 15 ; :: thesis: verum