def strip
      vars1, values1, term1 = @dest.strip
      vars2, values2, term2 = @n.strip
      return vars1 + vars2, values1 + values2, Random.new( term1, term2 )
    end
def strip
      vars1, values1, term1 = @dest.strip
      vars2, values2, term2 = @n.strip
      return vars1 + vars2, values1 + values2, Random.new( term1, term2 )
    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