thus Sum (digits (3880,10)) = (Sum <%0,8,8%>) + (Sum <%3%>) by Th716, AFINSQ_2:55
.= ((Sum <%0,8%>) + (Sum <%8%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((0 + 8) + (Sum <%8%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((0 + 8) + 8) + (Sum <%3%>) by AFINSQ_2:53
.= 16 + 3 by AFINSQ_2:53
.= 19 ; :: thesis: verum