The 1C opening is the key to the system. It's the most difficult and the most interesting, and a good place to start. None of the rest makes sense without this.
It's probably OK to open a limited hand with a nonforcing bid in a short suit. If responder can't find a bid the opponents can probably make something, so undoubled undertricks are no great worry. Opening a strong hand in a short suit if more problematical. Assuming you open a hand with four cards in each major, three diamonds, and two clubs, of about 18 HCP, with a bid of 1C, as many afficianados of five-card majors do these days, there are good arguments for the club bid to be forcing.
If the 1C bid is to be forcing, perhaps we can give it a greater load. In Polish Club, all hands of 19 or more points are opened 1C, in addition to a lot of the hands everyone else opens 1C. (In older versions of Polish 1C was limited to 22 or so HCP, and stronger hands were opened 2C. In more modern versions, 2C shows a minimum club 1-suiter, freeing up the 2C rebid for strong hands. AUC follows the latter model.)
Polish Club uses a strong (a good 15 to 18 HCP) 1NT opening. The author prefers a weak notrump. In addition, the Polish organization of rebids after 1C-1D can be improved upon. Finally, the author has never been fond of Precision's 2C opening, which Polish Club uses practically without modification. The following structure attempts a significant improvement over regular Polish club, without resorting to the profligate use of relays (for which, see Ron Klinger's "Power System").
There are basically three kinds of hands opened 1C in AUC. These are (1) "Strong Club" hands -- hands of 19 or more HCP, or a little less with compensating playing strength; (2) "strong notrump" hands -- balanced hands with 15-18 HCP and less than four diamonds; and (3) "club" hands -- hands with a real club suit. Each variety occurs about a third of the time. The balanced hands may contain a 5-card club suit, but not a 5-card major suit (and of course not a 4-card or longer diamond suit). The club hands are of several kinds. There are hands with 5 or more clubs and a 4-card major; three-suiters with a singleton diamond; and club 1-suiters too strong to open 2C (which is limited to at most a bad 15 HCP). In addition, we throw in hands with 6 diamonds, 4 clubs, and 16-18 HCP or the equivalent, since there is a convenient rebid for them.
There follows a list of responses to the 1C opening, with the requirements for each. For a discussion of the ensuing auction, select the desired response.
1D may the most common response. It is negative but not very negative -- up to 5 HCP or even a bad 6 with a 4-card major, and up to 9 HCP without one. This "1D threshold" is lower in AUC than in similar systems for a couple of good reasons. First, the 1C opening tends to be a bit stronger, because of the weak notrump. Second, the major-suit rebids after 1C-1D may be the weakest part of the system, so it pays to make them rare.
By the way, there is a lot to be said for responding 1D on all hands of, say, 17+ HCP. Responder could jump in notrump on the next round to show this stronger hand. This is probably not legal in most ACBL competitions and will have to wait for another edition of the system.The major-suit responses are pretty frequent as well. They are forcing, unlimited, and show at least 6 good HCP and a 4-card major, or a little less with nice distribution and high-card structure. Bidding proceeds almost as in standard systems, and is quite different from the bidding over the negative.
The 1NT response shows a balanced 10-12 HCP and denies a 4-card major, although a 5-card minor may be held. The negative 1D seems the right place to put 6-9 HCP balanced hands.
The 2C response is essentially an inverted raise. Responder needs 10 HCP or the equivalent in distribution and at least five clubs; or game-forcing values and at least four good clubs. Responder will be balanced or have a 4-card major only with 13+ HCP.
Bidding after the 2C response is usually pretty easy, since opener usually has clubs. Things are not as nice after the 2D response. The requirements are threrfore a little stricter. Responder will always have at least 5 diamonds, and will have a 4-card major or 5332 distribution only with game-forcing values.
The jumps to two of a major use up a lot of space. Since 1D is available for very weak hands, and we have other ways of bidding very strong hands, AUC borrows a trick from Polish Club and makes these jumps essentially weak 2-bids. Opener uses whatever methods are in place over weak twos. Note that if responder is a passed hand, the suit will be very weak, since there was a chance to bid a weak 2 on the previous round. These bids take some of the strain off of the 1M responses.
The jump to 2NT shows an even stronger hand than 1NT. Responder has 13 or more HCP, always 4333 or 4432, without a 4-card major.
Higher responses are essentially preemptive. They show a long broken suit without the values for a positive. In particular, 3C shows 6 or more clubs without the values for a positive. Since 2C is strong and 3C is weak, these are essentially inverted minor raises.