thus Sum (digits (4950,10)) =
(Sum <%0,5,9%>) + (Sum <%4%>)
by Th1373, AFINSQ_2:55
.=
((Sum <%0,5%>) + (Sum <%9%>)) + (Sum <%4%>)
by AFINSQ_2:55
.=
((0 + 5) + (Sum <%9%>)) + (Sum <%4%>)
by AFINSQ_2:54
.=
((0 + 5) + 9) + (Sum <%4%>)
by AFINSQ_2:53
.=
14 + 4
by AFINSQ_2:53
.=
18
; verum