Hi,

it appears that you need a

(put 'slime-space 'delete-selection t)

after the definition of `slime-space' to make it collaborate with `delete-selection-mode' and `CUA-mode'. (See also the recent discussion regarding this on emacs-pretest-bugs.)

Note that the above is not enough to make Undo behave correctly: after you have overwritten the region with a space, undoing the operation will only delete the space. It seems that Undo needs to understand that inserting the space is an atomic operation. I don't understand how undo works, so I can't offer a fix.

- David

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