thus Sum (digits (2134,10)) = (Sum <%4,3,1%>) + (Sum <%2%>) by Th896, AFINSQ_2:55
.= ((Sum <%4,3%>) + (Sum <%1%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((4 + 3) + (Sum <%1%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((4 + 3) + 1) + (Sum <%2%>) by AFINSQ_2:53
.= 8 + 2 by AFINSQ_2:53
.= 10 ; :: thesis: verum