
theorem Th31:
Sum digits(80,10) = 8
proof
  thus Sum digits(80,10) = Sum <%0%>+Sum <%8%> by Th30,AFINSQ_2:55
  .= 0 + Sum <%8%> by AFINSQ_2:53
  .= 8 by AFINSQ_2:53;
end;
