
theorem Th254:
Sum digits(374,10) = 14
proof
  thus Sum digits(374,10) = Sum <%4,7%>+Sum <%3%> by Th253,AFINSQ_2:55
  .= (4 + 7) + Sum <%3%> by AFINSQ_2:54
  .= 11 + 3 by AFINSQ_2:53
  .= 14;
end;
