The =dead-var-elim= component of the [[Stratego optimizer]] eliminates variables from a strategy expression if they are not used in a build.
For example, in the expression
<verbatim>
  { x, y, z :
	 ?F(x, y)
	 ; !y
	 ; ?G(z)
	 ; !H(z, z)
  }
</verbatim>
the variable =z= is used in the final build (not dead), and =y= is used in the build needed for the match with =G= (not dead).
However, =x= is dead since it does not contribute to the final result. 
Dead variable elimination removes dead variables by 

	* eliminating them from the scope, and
	* replacing occurrences in matches with a wildcard

Thus, the example reduces to
<verbatim>
  { y, z :
	 ?F(_, y)
	 ; !y
	 ; ?G(z)
	 ; !H(z, z)
  }
</verbatim>
Variable only matches (=?x=) with dead variables are turned into wildcard matches (=?_=) and can
be cleaned up by a subsequent simplification.

-- Main.EelcoVisser - 17 Aug 2003