thus Sum (digits (3550,10)) =
(Sum <%0,5,5%>) + (Sum <%3%>)
by Th1269, AFINSQ_2:55
.=
((Sum <%0,5%>) + (Sum <%5%>)) + (Sum <%3%>)
by AFINSQ_2:55
.=
((0 + 5) + (Sum <%5%>)) + (Sum <%3%>)
by AFINSQ_2:54
.=
((0 + 5) + 5) + (Sum <%3%>)
by AFINSQ_2:53
.=
10 + 3
by AFINSQ_2:53
.=
13
; verum