
theorem Th25:
Sum digits(50,10) = 5
proof
  thus Sum digits(50,10) = Sum <%0%>+Sum <%5%> by Th24,AFINSQ_2:55
  .= 0 + Sum <%5%> by AFINSQ_2:53
  .= 5 by AFINSQ_2:53;
end;
