[antlr-interest] Enforcing that a statement parm is only specified one time

[Brisard, Fred D]

Is there a standard pattern for allowing a single instance of a phrase
on a given statement?

For example, I have statement of the syntax of

Stmtname [keyword1 keyvalue1] [keyword2 keyvalue2]

I want to allow keyword1 or keyword2 to be specified in any order but I
don't want to allow the specification of either keyword more than once.

I have some statements with up to 8 different keywords that should only
occur once but in any order.

Thanks for any suggestions.

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