
theorem Th316:
Sum digits(475,10) = 16
proof
  thus Sum digits(475,10) = Sum <%5,7%>+Sum <%4%> by Th315,AFINSQ_2:55
  .= (5 + 7) + Sum <%4%> by AFINSQ_2:54
  .= 12 + 4 by AFINSQ_2:53
  .= 16;
end;
