/* fibonacci */

/* F_0 = 0 */
/* F_1 = 1 */
/* F_n = F_{n-1} + F_{n-2} */

/*
return e;
return t-t;
return t-(e);
return t-(0-t);
return c-(0-c);
return mref()-(0-mref());
return t.id()-(0-t.id());
return (e).id()-(0-(e).id());
return (t-t).id()-(0-(t-t).id());
return (this-1).fib()-(0-(this-2).fib());
*/

method fib()
	if this < 2 then return this; end;
	return (this-1).fib()-(0-(this-2).fib());
end;