user1855: [FEN ""]

1. d4 d6 2. e4 g6 3. Nc3 Nf6 4. Nf3 c5 5. dxc5 Qa5 6. cxd6

Above you can see the first moves of a Pirc Defense game. To study this opening, I learn with the book "Pirc Alert!" by Lev Alburt and Alex Chernin.
After 4. Nf3, there is a trick which consists of ...c5, ...Qa5 (two pawns are threatened) and ...Qxc5, winning the pawn, ...c5 and bringing a Sicilian Dragon pawn structure, which is very good. But today I played an Internet game (seen above) and White's move 6. cxd6 seems very good. The authors of my book didn't speak about this move.
I had over viewed the position after 6. dxc6 and neither I nor my chess engine. could find any strong reply.
Is the move 6... exd6 strong? What is Black's best reply to 6. cxd6?

user2001: I play like this with the white pieces
[FEN ""]
1. d4 d6 2. e4 Nf6 3. Nc3 g6 4.h3 Bg7 5.Nf3 O-O 6.Bd3

As far as I understand, black already has a "dragon structure" because the dragon pawn chain is h7-g6-f7-e7-d6 and has nothing to do with the c-pawn. It is true that the Dragon variation is found in the Sicilian system. But the dragon pawn structure has nothing to do with the c-pawn to my knowledge. As for the c7-c5 push in this system, usually black prefers c7-c6 instead, preparing b7-b5, opening the c7-square for the queen and taking control over the d5-square.

user4543: Black gets his pieces to attacking posts after cxd6. Nxe4 is a good reply and Black threatens to take multiple times on c3. The extra pawn isn't that important compared with the relative quality of Black's pieces. Bg7 Nc6 and Bg4 are coming with good development and chances for the Black player.

user14079: ...c5 followed by ...Qa5 is indeed a very important trick in the Pirc defense in order to reach a dragonlike pawn structure.
However, it can only work after you have developed your bishop to g7, adding pressure on the dark squares.
Compare
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
1. d4 d6 2. e4 Nf6 3. Nc3 g6 4. Nf3 Bg7 5. Be2 c5 6. dxc5 Qa5 7. cxd6? Ne4!

where Black has a huge advantage.
With 
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
1. d4 d6 2. e4 Nf6 3. Nc3 g6 4. Nf3 c5? 5. dxc5 Qa5 6. cxd6 Ne4?! 7.Qd4! Nf6 (7...Nxc3 8. Qxh8!) 8.dxe7 Bxe7 9.Bg5 Nc6 10.Bb5 

White wins because the fork on h8 and e4 refutes Black premature display of activity, and she will keep at least one extra pawn. 7...Nxc3 can be countered simply by 9.bc3, but more audaciously by 8.Qxh8! when no discovered check brings any relief to Black for her huge material loss.
7...Nf6 saves the piece but not the game after 8.dxe7 Bxe7 9.Bg5 Nc6 10.Bb5, when White has a full extra pawn and some initiative.

user4362: Yeah, seems like black just blundered a pawn with c5.
Probably you just mixed up the variation and you really wanted to play:
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
1. d4 d6 2. e4 Nf6 3. Nc3 g6 4. f4 Bg7 5. Nf3 c5  

That is quite a common variation, I looked at 6.dc Qa5 7.Qd4 for white a while back, if I remember correctly. So maybe you should just check your book again, it's unlikely they made such a mistake.

1855: <pre><code>[FEN ""]

1. d4 d6 2. e4 g6 3. Nc3 Nf6 4. Nf3 c5 5. dxc5 Qa5 6. cxd6
</code></pre>

<p>Above you can see the first moves of a Pirc Defense game. To study this opening, I learn with the book "Pirc Alert!" by Lev Alburt and Alex Chernin.</p>

<p>After 4. Nf3, there is a trick which consists of ...c5, ...Qa5 (two pawns are threatened) and ...Qxc5, winning the pawn, ...c5 and bringing a Sicilian Dragon pawn structure, which is very good. But today I played an Internet game (seen above) and White's move 6. cxd6 seems very good. The authors of my book didn't speak about this move.</p>

<p>I had over viewed the position after 6. dxc6 and neither I nor my chess engine. could find any strong reply.</p>

<p>Is the move 6... exd6 strong? What is Black's best reply to 6. cxd6?</p>
 2001: <p>I play like this with the white pieces</p>

<pre><code>[FEN ""]
1. d4 d6 2. e4 Nf6 3. Nc3 g6 4.h3 Bg7 5.Nf3 O-O 6.Bd3
</code></pre>

<p>As far as I understand, black already has a "dragon structure" because the dragon pawn chain is h7-g6-f7-e7-d6 and has nothing to do with the c-pawn. It is true that the Dragon variation is found in the Sicilian system. But the dragon pawn structure has nothing to do with the c-pawn to my knowledge. As for the c7-c5 push in this system, usually black prefers c7-c6 instead, preparing b7-b5, opening the c7-square for the queen and taking control over the d5-square.</p>
 4543: <p>Black gets his pieces to attacking posts after cxd6. Nxe4 is a good reply and Black threatens to take multiple times on c3. The extra pawn isn't that important compared with the relative quality of Black's pieces. Bg7 Nc6 and Bg4 are coming with good development and chances for the Black player.</p>
 14079: <p>...c5 followed by ...Qa5 is indeed a very important trick in the Pirc defense in order to reach a dragonlike pawn structure.</p>

<p>However, it can only work <em>after</em> you have developed your bishop to g7, adding pressure on the dark squares.</p>

<p>Compare</p>

<pre><code>rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
1. d4 d6 2. e4 Nf6 3. Nc3 g6 4. Nf3 Bg7 5. Be2 c5 6. dxc5 Qa5 7. cxd6? Ne4!
</code></pre>

<p>where Black has a huge advantage.</p>

<p>With </p>

<pre><code>rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
1. d4 d6 2. e4 Nf6 3. Nc3 g6 4. Nf3 c5? 5. dxc5 Qa5 6. cxd6 Ne4?! 7.Qd4! Nf6 (7...Nxc3 8. Qxh8!) 8.dxe7 Bxe7 9.Bg5 Nc6 10.Bb5 
</code></pre>

<p>White wins because the fork on h8 and e4 refutes Black premature display of activity, and she will keep at least one extra pawn. 7...Nxc3 can be countered simply by 9.bc3, but more audaciously by 8.Qxh8! when no discovered check brings any relief to Black for her huge material loss.</p>

<p>7...Nf6 saves the piece but not the game after 8.dxe7 Bxe7 9.Bg5 Nc6 10.Bb5, when White has a full extra pawn and some initiative.</p>
 4362: <p>Yeah, seems like black just blundered a pawn with c5.
Probably you just mixed up the variation and you really wanted to play:</p>

<pre><code>rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
1. d4 d6 2. e4 Nf6 3. Nc3 g6 4. f4 Bg7 5. Nf3 c5  
</code></pre>

<p>That is quite a common variation, I looked at 6.dc Qa5 7.Qd4 for white a while back, if I remember correctly. So maybe you should just check your book again, it's unlikely they made such a mistake.</p>
