Consider the following sample:
Join[{A[x]}, {A[x]}, 2]
It causes Join::headsd
warning in and before v9 and returns the input:
Join::headsd: Expression
{A[x]}
at position1
is expected to have headList
for all subexpressions through level2
.
But gives the following output without warning at least since v11.2:
(* {A[x, x]} *)
What's funny is, it's mentioned in the Details of Join
since v10, that:
The $\text{list}_i$ do not need to have head
List
, but must all have the same head.
So my question is, is this an intentional change i.e. a mistake in the document of Join
, or a bug of Join
?
If it's intentional, is it possible to bring back the old behavior?
If it's a bug, what's the easiest fix for it?
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