thus Sum (digits (1452,10)) = (Sum <%2,5,4%>) + (Sum <%1%>) by Th840, AFINSQ_2:55
.= ((Sum <%2,5%>) + (Sum <%4%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((2 + 5) + (Sum <%4%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((2 + 5) + 4) + (Sum <%1%>) by AFINSQ_2:53
.= 11 + 1 by AFINSQ_2:53
.= 12 ; :: thesis: verum