Free energy of a two-state system

[Shackleford]

What am I missing? The manual has the second term of the free energy as (\epsilon/\tau)/[1 + exp(\epsilon/\tau)]

Not sure why my Greek letters are superscripts.

http://i111.photobucket.com/albums/n149/camarolt4z28/IMG_20110228_183953.jpg?t=1298940684

http://i111.photobucket.com/albums/n149/camarolt4z28/IMG_20110228_184741.jpg?t=1298940701

http://i111.photobucket.com/albums/n149/camarolt4z28/IMG_20110228_184751.jpg?t=1298940709