thus Sum (digits (1364,10)) = (Sum <%4,6,3%>) + (Sum <%1%>) by Th832, AFINSQ_2:55
.= ((Sum <%4,6%>) + (Sum <%3%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((4 + 6) + (Sum <%3%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((4 + 6) + 3) + (Sum <%1%>) by AFINSQ_2:53
.= 13 + 1 by AFINSQ_2:53
.= 14 ; :: thesis: verum