thus Sum (digits (2980,10)) = (Sum <%0,8,9%>) + (Sum <%2%>) by Th626, AFINSQ_2:55
.= ((Sum <%0,8%>) + (Sum <%9%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 8) + (Sum <%9%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 8) + 9) + (Sum <%2%>) by AFINSQ_2:53
.= 17 + 2 by AFINSQ_2:53
.= 19 ; :: thesis: verum