TITLE: formal differences?
QUESTION [6 upvotes]: Hi,
given a local ring $A$ with maximal ideal $m$ which are differences between $Spec(\hat{A})$ ($\hat{A}$ completion of $A$ along $m$) and $Spf(A)$?

REPLY [4 votes]: There is a nice introduction to formal schemes in Luc Illusie's section of the book ``Fundamental Algebraic Geometry (Grothendieck's FGA Explained)''.  Recommend!