# what does matroid structure mean in this answer?

what does matroid structure mean in the answer to this question? I looked it up in Wikipedia but don't know which part applies to this case. What does the reply mean by "verify something forms a matroid structure"?

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David's answer describes exactly what this means immediately below that sentence. –  Qiaochu Yuan May 30 '12 at 21:08
It means precisely that the points 1. 2. and 3. given in the answer there are satisfied. –  Alastair Litterick May 30 '12 at 21:08
For future reference, you could have asked this as a comment under David's answer. –  Rahul May 30 '12 at 21:13
@Qiaochu/Alastair: Thank you! –  cody May 30 '12 at 21:16