Vertical lines for delimiting chunks of text

[Paul A Blampied]

Delimiting definitions, theorems, etc.
--------------------------------------

I would like to have the following mechanism for displaying definitions,
theorems etc.:

Normally they appear like

Theorem 1
XXXXXXXXXXXXX
XXXXXXXXXXXXX
XXXXXXXXXXXXX
Proof:
XXXXXXXXXXXXX
XXXXXXXXXXXXX
XXXXXXXXXXXXX

But I would like to indent them slightly and add a vertical line down the
left side, and a small horizontal line at the bottom to signal the end of
the definition, theorem, etc.:

Theorem 1
| XXXXXXXXXXXXX
| XXXXXXXXXXXXX
| XXXXXXXXXXXXX
| Proof:
| XXXXXXXXXXXXX
| XXXXXXXXXXXXX
| XXXXXXXXXXXXX
|____

And it should also be able to cope with page or column breaks, eg.

Theorem 1
| XXXXXXXXXXXXX
| XXXXXXXXXXXXX
--- page break ---
| XXXXXXXXXXXXX
| Proof:
| XXXXXXXXXXXXX
| XXXXXXXXXXXXX
| XXXXXXXXXXXXX
|____


I managed to write a macro that prints "|" at the left of each row and
then some "_"'s at the end of the block, but it would be better to have
the lines in PostScript/PDF graphics.

Can anybody give me some hints...!?

        Paul Blampied