I do not have an answer to your question, but your answer led me to
exploring agenda in the following way because you are using * to
trigger the option of your agenda. The result I get was unintuitive.
In particular I didn't understand how y=_1 produces 1 in my example.
But now I see why and that is quite interesting that the _1 behaves
like it would in _1&{ .
_1:`0:`1:@.]"0] 0 1 _1
_1 0 1
Thank you.
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