def strip
      meta_vars, meta_values, var = @index.strip
      vars, values, term = @term.subst( @index => var ).strip
      return vars + meta_vars, values + meta_values, Lambda.new( var, term )
    end
def strip
      meta_vars, meta_values, var = @index.strip
      vars, values, term = @term.subst( @index => var ).strip
      return vars + meta_vars, values + meta_values, Lambda.new( var, term )
    end
Strip of all values

 Split up into variables, values, and a term where all values have been
 replaced with variables.

 @return [Array<Array,Node>] Returns an array of variables, an array of
 values, and the term based on variables.

 @private