def element( i )
      values = @values.collect do |value|
        value.dimension == 0 ? value : value.element( i )
      end
      self.class.new( *values ).demand
    end
def element( i )
      values = @values.collect do |value|
        value.dimension == 0 ? value : value.element( i )
      end
      self.class.new( *values ).demand
    end
Get element of unary operation

 @param [Integer,Node] i Index of desired element.

 @return [Node,Object] Element of unary operation.

 @private