This even originates from the upper-level function of this anonymous function. An actual parameter (even) is passed when the upper-level function is called, so the row parameters of this anonymous function can be used.
reply$a = function() { return 111 };
$a(even)
The number of actual parameters can be greater than the formal parameters, so it doesn't matter whether you write it or not.
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This even originates from the upper-level function of this anonymous function. An actual parameter (even) is passed when the upper-level function is called, so the row parameters of this anonymous function can be used.
This is just a formal parameter