
theorem Th23:
Sum digits(40,10) = 4
proof
  thus Sum digits(40,10) = Sum <%0%>+Sum <%4%> by Th22,AFINSQ_2:55
  .= 0 + Sum <%4%> by AFINSQ_2:53
  .= 4 by AFINSQ_2:53;
end;
