thus Sum (digits (3075,10)) = (Sum <%5,7,0%>) + (Sum <%3%>) by Th1241, AFINSQ_2:55
.= ((Sum <%5,7%>) + (Sum <%0%>)) + (Sum <%3%>) by AFINSQ_2:55
.= ((5 + 7) + (Sum <%0%>)) + (Sum <%3%>) by AFINSQ_2:54
.= ((5 + 7) + 0) + (Sum <%3%>) by AFINSQ_2:53
.= 12 + 3 by AFINSQ_2:53
.= 15 ; :: thesis: verum