diff --git a/preface.asciidoc b/preface.asciidoc
index eefaeded..ed794fd0 100644
--- a/preface.asciidoc
+++ b/preface.asciidoc
@@ -19,7 +19,7 @@ _The best way to get the right answer on the Internet is not to ask a question,
I hope you can help me find and publish the "right answer" by the time this book is ready to print.
-The early-realease source code is published on Github: https://github.com/aantonop/bitcoinbook
+The early-release source code is published on Github: https://github.com/aantonop/bitcoinbook
File an "Issue", or fork, modify and create a "Pull Request" with your changes.
@@ -74,7 +74,7 @@ pass:[product mixes] and pricing programs for pass:[organizations], pass:[government agencies], and pass:[individuals]. Subscribers have access to thousands of books, training videos, and prepublication manuscripts in one fully searchable database from publishers like O’Reilly Media, Prentice Hall Professional, Addison-Wesley Professional, Microsoft Press, Sams, Que, Peachpit Press, Focal Press, Cisco Press, John Wiley & Sons, Syngress, Morgan Kaufmann, IBM Redbooks, Packt, Adobe Press, FT Press, Apress, Manning, New Riders, McGraw-Hill, Jones & Bartlett, Course Technology, and dozens pass:[more]. For more information about Safari Books Online, please visit us pass:[online].
+Safari Books Online offers a range of pass:[product mixes] and pricing programs for pass:[organizations], pass:[ government agencies], and pass:[individuals]. Subscribers have access to thousands of books, training videos, and prepublication manuscripts in one fully searchable database from publishers like O’Reilly Media, Prentice Hall Professional, Addison-Wesley Professional, Microsoft Press, Sams, Que, Peachpit Press, Focal Press, Cisco Press, John Wiley & Sons, Syngress, Morgan Kaufmann, IBM Redbooks, Packt, Adobe Press, FT Press, Apress, Manning, New Riders, McGraw-Hill, Jones & Bartlett, Course Technology, and dozens pass:[more]. For more information about Safari Books Online, please visit us pass:[online].
=== How to Contact Us
@@ -141,8 +141,8 @@ difficulty target::
((("target difficulty")))
A difficulty at which all the computation in the network will find blocks approximately every 10 minutes.
-difficulty re-targetting::
-((("difficulty re-targetting")))
+difficulty re-targeting::
+((("difficulty re-targeting")))
A network-wide re-calculation of the difficulty which occurs once every 2106 blocks and considers the hashing power of the previous 2106 blocks.
fees::