thus Sum (digits (1240,10)) = (Sum <%0,4,2%>) + (Sum <%1%>) by Th452, AFINSQ_2:55
.= ((Sum <%0,4%>) + (Sum <%2%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((0 + 4) + (Sum <%2%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((0 + 4) + 2) + (Sum <%1%>) by AFINSQ_2:53
.= 6 + 1 by AFINSQ_2:53
.= 7 ; :: thesis: verum