In back of, in between. Incorrect?

[Cisco795]

"In the back of the library is Allen Hall".
"Mary was standing in between two chairs".

Should I omit the word "in" in both sentences?

God Bless you.
Cisco.
_________________
Please, always correct me if I have made any kind of mistakes in my posts.

[Yankee]

Hi Cisco

[Molly]

[Diverhank]

[Yankee]

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Cisco's question was about whether "in" is necessary or not. However, in the "Allen Hall" example, I was not sure whether Cisco was referring to a person or the name of a building (on a university campus, for example). For me, the meaning of the phrase changes depending on whether the word "the" is included or not. I mentioned it seemed unlikely that a building called "Allen Hall" would be located inside the library, at the rear (which in my mind would be "in the back of").

The title of Cisco's thread did not include the word "the", however the question in his post did. So, we'll have to wait for Cisco to clarify his question, I suppose.
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[Cisco795]

[Yankee]

Hi Cisco

You posted two different phrases:
- in the back of
- in back of

The phrase "in the back of" suggests "inside, near/at the back"

The phrase "in back of" means "behind" (i.e. not inside).
Look at definition 54 here:
http://dictionary.reference.com/search?q=in+back+of&r=66
You can also find "in back of" in Webster's Dictionary as well as here:
http://dictionary.cambridge.org/define.asp?key=back*3+1&dict=A

I would use the word "in" for both expressions.

I presume that Molly was attempting to tell us that "in back of" is never used in British English.
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[Molly]