thus Sum (digits (3925,10)) = (Sum <%5,2,9%>) + (Sum <%3%>) by Th1291, AFINSQ_2:55
.= ((Sum <%5,2%>) + (Sum <%9%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((5 + 2) + (Sum <%9%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((5 + 2) + 9) + (Sum <%3%>) by AFINSQ_2:53
.= 16 + 3 by AFINSQ_2:53
.= 19 ; :: thesis: verum