thus Sum (digits (2050,10)) = (Sum <%0,5,0%>) + (Sum <%2%>) by Th1179, AFINSQ_2:55
.= ((Sum <%0,5%>) + (Sum <%0%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((0 + 5) + (Sum <%0%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((0 + 5) + 0) + (Sum <%2%>) by AFINSQ_2:53
.= 5 + 2 by AFINSQ_2:53
.= 7 ; :: thesis: verum