Dan Gun
Dan Gun mostly follows Heian Shodan (Pinan Nidan), but places the techniques in opposite ends of the pattern.
The following videos were used as reference:
ITF Legacy performance of Dan Gun.
Hirokazu Kanazawa performing Heian Shodan.
Thomas Geiger performing Pinan Nidan.
**Updated 30 December 2017**
All punches in Dan Gun, the 2nd proper pattern, are high section punches. All punches in Taikyoku Nidan, the 2nd Shotokan kihon kata, are high section. This may be coincidental, but I find it interesting and worth noting.
The opening movements of Dan Gun closely resemble the closing movements of Heian Shodan. They begin with knife hand blocks.
Both knife hand blocks are followed by a step forward, with a punch in Dan Gun and an additional knife hand in Heian Shodan at a 45 degree angle. Both patterns repeat this on both sides.
Dan Gun then turns to the North into a front stance with a low block, while this movement is done later in Heian Shodan facing to the South. Both patterns follow this with three punches while stepping forward.
Dan Gun follows with a twin forearm block, which is the opening move of Heian Nidan, but the sequence is different and I do not consider it significant. It's possible that the designers believed that this technique must be introduced in the 2nd pattern of the Chang Hon series because it's in the 2nd pattern of the Heian series, but felt Won Hyo was too difficult to be placed 2nd, so they included the twin forearm in Dan Gun. This is, of course, wild speculation.
Dan Gun then turns to the South with a low block and high block in place, followed by three more high blocks while stepping forward. (shown here from a side angle).
This is similar to how it is performed in Heian Shodan, though from the other direction. Most styles perform it with a low block, followed by three high blocks while stepping.
In Shotokan (or, at least, how Kanazawa performs it here), the chambering motion for the next high block resembles the position of another block, but this is done while stepping.
Intrestingly, Choi's 1965 directions for"HEI-AN PATTERN I" describe two distinct blocks (6 & 7) before stepping, which means that Dan Gun is done the same way that Choi practiced Heian Shodan.
The endings of both Dan Gun and Do San are interesting in that they resemble the endings of other variations of Heian Shodan, particularly those that call the pattern Pinan Nidan.
Dan Gun ends with a reverse knife hand strike, then steps into a punch, repeated on both sides.
Pinan Nidan often ends with a spear hand in a similar stance, followed by a step forward into another, repeated on both sides.