Nonfiction book question

You can try to sell books wherever you like. There's no rule which says you can't.

However, you will probably find it difficult to sell two books on exactly the same subject to two separate publishers, but if you write them both well enough and give each a different slant, you should be ok so long as the publication dates are separated enough; and so long as your contracts don't prohibit this (which can sometimes happen).

Just don't try to write the same book twice over. That won't work at all.

Alison, you've started a nearly identical thread elsewhere on AW, so I'm going to lock this one now.