### Ogdens lemma

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**Ogden's lemma**

Let L be a Context Free Language. Then
there is a constant n such that if z is any word in L, and we mark any n or
more positions of z “distinguished” then we can write z = uvwxy such that:

(1) v and x together have atleast one distinguished
position.

(2) vwx has at most n distinguished positions and

(3) for all i>=0 uv

^{i}wx^{i}y is in L.
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