thus Sum (digits (1850,10)) = (Sum <%0,5,8%>) + (Sum <%1%>) by Th1167, AFINSQ_2:55
.= ((Sum <%0,5%>) + (Sum <%8%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((0 + 5) + (Sum <%8%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((0 + 5) + 8) + (Sum <%1%>) by AFINSQ_2:53
.= 13 + 1 by AFINSQ_2:53
.= 14 ; :: thesis: verum