thus Sum (digits (3725,10)) = (Sum <%5,2,7%>) + (Sum <%3%>) by Th1279, AFINSQ_2:55
.= ((Sum <%5,2%>) + (Sum <%7%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((5 + 2) + (Sum <%7%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((5 + 2) + 7) + (Sum <%3%>) by AFINSQ_2:53
.= 14 + 3 by AFINSQ_2:53
.= 17 ; :: thesis: verum