
theorem Th213:
Sum digits(400,10) = 4
proof
  thus Sum digits(400,10) = Sum <%0,0%>+Sum <%4%> by Th212,AFINSQ_2:55
  .= (0 + 0) + Sum <%4%> by AFINSQ_2:54
  .= 4 by AFINSQ_2:53;
end;
