Thue systems are bidirectional in this sense: for every u → w, there is
also a w ← u. A system which is unidirectional, in which the
replacements only occur in one direction, is called a _semi-Thue system_.
+ type: Mathematical Object
+ Bitcoin is an experimental digital currency.
+ It was designed to eliminate the human element from its economy.
+ Its valuation is exactly as stable as you'd expect it to be from that.
+ - 'http://rationalwiki.org/wiki/Bitcoin'