As with many other ellipsis mechanisms, stripping challenges theories of syntax in part because the elided material often fails to qualify as a constituent in a straightforward manner.
Each time, the elided material appears in the non-initial conjunct of the coordinate structure.
[4] The fact that gapping and stripping are alike in these respects does indeed suggest that they are one and the same ellipsis mechanism.
The remnant in the stripped clause is introduced by not and the entire sentence functions to correct a mistaken assumption in the preceding context.
The aspect of not-stripping that remains mysterious concerns the obligatory position of not before the (first) remnant.
: As with most ellipsis mechanisms, theoretical accounts of stripping face significant challenges.
The constituency vs. dependency distinction is therefore one avenue that one might pursue to locate an explanation of such cases.
Another avenue to explore for an explanation is to focus on the elided material (as opposed to on the remnant).
The object pronoun it in the a-tree and the indefinite article an in the b-tree are not linked directly to the other elided material.