thus Sum (digits (1342,10)) = (Sum <%2,4,3%>) + (Sum <%1%>) by Th830, AFINSQ_2:55
.= ((Sum <%2,4%>) + (Sum <%3%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((2 + 4) + (Sum <%3%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((2 + 4) + 3) + (Sum <%1%>) by AFINSQ_2:53
.= 9 + 1 by AFINSQ_2:53
.= 10 ; :: thesis: verum