"… a cardboard tube, more or less the same length as
the inner core of a toilet roll, but thicker. He frowned,
took the roll out, laid it on the desk and poked up it
with the butt end of a pencil. Something slid out.
It looked like a rolled-up black plastic dustbin liner;
but when he unfolded it, he recognised it as the funny
sheet thing he’d found in the strongroom and briefly
described as an Acme Portable Door, before losing
his nerve and changing it to something less facetious."
— Holt, Tom. The Portable Door . Orbit. Kindle Edition.
According to goodreads.com, the Holt book was
"first published March 6, 2003."
Compare and contrast the "portable door" as a literary device
with the "tesseract" in A Wrinkle in Time (1962).
See also this journal on March 6, 2003.