
theorem Th407:
Sum digits(780,10) = 15
proof
  thus Sum digits(780,10) = Sum <%0,8%>+Sum <%7%> by Th406,AFINSQ_2:55
  .= (0 + 8) + Sum <%7%> by AFINSQ_2:54
  .= 8 + 7 by AFINSQ_2:53
  .= 15;
end;
