variations in the manner of showing the number of controls, all of which are alertable. The following examples of responses are representative but by no means all-inclusive. 2 shows 0 or 1 control (at most 1 king), 2 shows 2 controls (1 ace or 2 kings), 2 shows 3 controls (specifically 1 ace and 1 king), 2NT shows 3 controls (specifically 3 kings), and 3 shows 4 controls, 3 or higher, etc. on up the line. With ace-showing responses, the responder bids the suit of the Ace, 2NT with two or more kings, and 2 with a king or less. With (unlikely) 2 aces, the responder bids 3. As a corollary, subsequent Blackwood by the opener asks for kings rather than aces. Either-or treatment Some players play that 2 can also contain a weak variant, for example the 2 weak two bid. In this scheme, 2 by responder is a waiting bid, asking the opener to describe his hand further if he is strong. If the opening hand has a weak two bid in diamonds, he should pass. However, if the responder has a strong hand, typically 15 high card points or more, he responds with 2NT. This treatment is often subject to restrictions in tournament play, as it has a destructive potential—see Bridge convention#Regulations. Advantages One major advantage of the artificial opening bid of 2 for all types of strong hands is that other opening bids at the two-level (2, 2 and 2) become available for weak two bids, thus eliminating many possible bids for the opponents. These weak two hands appear 20 times as often as the very strong hands, which illustrates the inefficiency of reserving all opening bids at the two-level for very strong hands. An alternative is to use strong two bids for hands which are strong but not game forcing, which reduces the range of one-level openings and helps bidding accuracy. However, since weak twos are so useful, there are methods which allow weak twos in hearts and spades and use 2 to show a different range of strong hands; these are Benjaminised (Benji) Acol, Reverse Benji and the Multicoloured Two Diamonds. Another advantage is the relative precision with which strong balanced hands can be bid. An opening bid of 2 NT indicates a balanced hand with 20-21 HCP in Standard American or 20-22 HCP in standard Acol, and for even stronger balanced hands, the