'CHAD PA
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Anyway, the la particle needs something on the right side to bind it to the left side, and this is 'chad pa. 'chad pa means explanation. The verb is actually 'chad, to teach, expound, explain. Note that there is another interpretation with the word 'chad, to be cut or broken, including a variation of 'chad pa that means cut into pieces or being separate.
Here again one needs to look at the context, we are dealing with a commentary, so there's a notion of explanations and teachings. So here 'chad pa is indeed about the explanation that is bound via la to the left side.