thus Sum (digits (1078,10)) = (Sum <%8,7,0%>) + (Sum <%1%>) by Th810, AFINSQ_2:55
.= ((Sum <%8,7%>) + (Sum <%0%>)) + (Sum <%1%>) by AFINSQ_2:55
.= ((8 + 7) + (Sum <%0%>)) + (Sum <%1%>) by AFINSQ_2:54
.= ((8 + 7) + 0) + (Sum <%1%>) by AFINSQ_2:53
.= 15 + 1 by AFINSQ_2:53
.= 16 ; :: thesis: verum