[FOM] A textbook on logic with natural deduction

[Peter Hancock]

Andrej Bauer wrote:

> ... , but I couldn't really find an _introductory_
> textbook that would cover logic in natural deduction style. Can
> someone recomment a good textbook or available lecture notes that are
> written in natural-deduction style (trees, not proof boxes, I know I
> should have used boxes... but it is too late for this year)? This is
> for a freshman course.

A Logical Approach to Discrete Math 
by David Gries and Fred. B. Schneider
has something(s) to recommend it, namely the
spirit of teaching logic as a tool, and 
a broad perspective including but not limited
to natural deduction. 

Gries may have some similar material at his
website:

http://www.cs.cornell.edu/gries/

Peter Hancock