Legal help in putting a wall up (3)

I believe the answer is:

law

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'legal help' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?

I can't explain the rest of the clue.

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(Other definitions for law that I've seen before include "Set of rules laid down by authority" , "Edict" , "Legislation" , "Rule prohibiting certain actions" , "Act" .)

I've seen this clue in the Evening Standard.

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