Prefigure worksheet

[davidaustinm]

These three commits are all to the sample article and:

• add an annotated PreFigure diagram to a worksheet, following up on Annotated PreFigure diagrams in worksheets #2820
• regenerate the existing PreFigure SVGs so that the value of all id attributes are unique
• adds the new PreFigure SVG for the worksheet

[rbeezer]

Thanks for adding a test inside a worksheet! Merged as-is, except the first commit was silently edited:

• Old projection1.png did not need to hang around. It projected a onto u.
• PreFigure image projects a onto b.
• I edited the problem statement to define the old u as the new b.
• I enjoyed doing some linear algebra.
• Thanks, Claude. I would probably have missed that.

[davidaustinm]

Oops, sorry about the typos! Thanks for catching and merging!

[rbeezer]

Ooops, no PDF image for the LaTeX build of the sample article. Likely been missing from the website for a few days. 70188ae

Discovered while working on #2827. All in the family.

A PNG is still also needed for EPUB.

[davidaustinm]

I sent a PNG in #2832. The PDF that was already merged looks good.

All in the family.

I think we know who's been playing the role of Meathead.

[rbeezer]

the role of Meathead

Ouch!

[davidaustinm]

I meant me! I feel like I've been a little sloppy lately.