
theorem Th419:
Sum digits(900,10) = 9
proof
  thus Sum digits(900,10) = Sum <%0,0%>+Sum <%9%> by Th418,AFINSQ_2:55
  .= (0 + 0) + Sum <%9%> by AFINSQ_2:54
  .= 9 by AFINSQ_2:53;
end;
