
theorem Th252:
Sum digits(357,10) = 15
proof
  thus Sum digits(357,10) = Sum <%7,5%>+Sum <%3%> by Th251,AFINSQ_2:55
  .= (7 + 5) + Sum <%3%> by AFINSQ_2:54
  .= 12 + 3 by AFINSQ_2:53
  .= 15;
end;
