thus Sum (digits (1562,10)) = (Sum <%2,6,5%>) + (Sum <%1%>) by Th848, AFINSQ_2:55
.= ((Sum <%2,6%>) + (Sum <%5%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((2 + 6) + (Sum <%5%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((2 + 6) + 5) + (Sum <%1%>) by AFINSQ_2:53
.= 13 + 1 by AFINSQ_2:53
.= 14 ; :: thesis: verum