A square dance program or square dance list is a set of defined square dance calls or dance steps which are associated with a level of difficulty. Programs and program lists are managed and universally recognized in modern western square dance. Upper-level dance programs include not only square dance calls, but also square dance concepts. CALLERLAB’s program lists CALLERLAB, the International Association of Square Dance Callers, the largest international square dance association manages the most universally recognized of these programs, and currently manages seven dance program lists. There are four main levels, some of which are divided into sublevels: Mainstream, Plus, Advanced (2 sub-levels), Challenge (5 sublevels, the top two levels of which are not managed). In general, the first three levels are more physically active than the challenge level (often referred to as challenge square dance). Challenge square dance is more cerebral and focuses on problem-solving. These program lists are not static, and there has always been some occasional adjustment of the programs. Today, the tendency is to reduce the number of steps at Mainstream, the lowest level, so that there is less required learning time to achieve a controlled common level of dancing proficiency. CALLERLAB's seven managed dance program lists, as of Aug. 2005, are as follows. After the name of the program is an indication of the number of steps added at each level, and the total number of steps and concepts one is expected to know after having learned the level: Advanced 1 and Advanced 2 are officially one program ("Advanced"), in some regions they are treated as two separate programs. CALLERLAB recognizes the first 53 calls of Mainstream as a separate program called "Basic". Higher-level programs are not maintained by any official group, although the National Advanced and Challenge Convention maintained a C3B list until it disbanded in 2000. At the present, the C3B list is informally maintained by consensus of the callers of that program. At the C4 level callers are generally free to use any call or concept they please (subject only to the patience and knowledge of their dancers), but efforts are made to collect and standardize those calls and concepts used by practising callers. A C4 dancer typically knows about 1000 calls and 100 concepts. "Hard" C4 level dancing is sometimes informally called C5. Other program lists There are also several lower-level programs promoted by groups other than Callerlab. For example,