thus Sum (digits (1936,10)) = (Sum <%6,3,9%>) + (Sum <%1%>) by Th880, AFINSQ_2:55
.= ((Sum <%6,3%>) + (Sum <%9%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((6 + 3) + (Sum <%9%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((6 + 3) + 9) + (Sum <%1%>) by AFINSQ_2:53
.= 18 + 1 by AFINSQ_2:53
.= 19 ; :: thesis: verum