code: private Expr determineVariableAliases(GlobalEnvironment environment,
  			Set<WyalFile.VariableDeclaration> freeVariables) {
  		Expr aliases = null;
  		for (WyalFile.VariableDeclaration var : freeVariables) {
  			WyalFile.VariableDeclaration parent = environment.getParent(var);
  			if (parent != null) {
  				// This indicates a variable alias, so construct the necessary
  				// equality.
  				Expr.VariableAccess lhs = new Expr.VariableAccess(var);
  				Expr.VariableAccess rhs = new Expr.VariableAccess(parent);
  				Expr aliasEquality = new Expr.Equal(lhs, rhs);
  				//
  				aliases = and(aliases, aliasEquality);
  			}
  		}
  		return aliases;
  	}
docs: Determine any variable aliases which need to be accounted for. This is done
  by adding an equality between the aliased variables to ensure they have the
  same value.
  
  @param environment
  @param freeVariables
  @return