thus Sum (digits (1430,10)) = (Sum <%0,3,4%>) + (Sum <%1%>) by Th838, AFINSQ_2:55
.= ((Sum <%0,3%>) + (Sum <%4%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((0 + 3) + (Sum <%4%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((0 + 3) + 4) + (Sum <%1%>) by AFINSQ_2:53
.= 7 + 1 by AFINSQ_2:53
.= 8 ; :: thesis: verum