
theorem Th320:
Sum digits(513,10) = 9
proof
  thus Sum digits(513,10) = Sum <%3,1%>+Sum <%5%> by Th319,AFINSQ_2:55
  .= (3 + 1) + Sum <%5%> by AFINSQ_2:54
  .= 4 + 5 by AFINSQ_2:53
  .= 9;
end;
