def minus(x,y=nil)
      
      return (y.nil?) ? Rubyvis::Vector.new(@x - x.x, @y - x.y) : Rubyvis::Vector.new(@x - x, @y - y)
    end
def minus(x,y=nil)
      
      return (y.nil?) ? Rubyvis::Vector.new(@x - x.x, @y - x.y) : Rubyvis::Vector.new(@x - x, @y - y)
    end
Returns this vector minus the vector <i>v</i>: <i>&#x27e8;x - v.x, y -
 v.y&#x27e9;</i>. If only one argument is specified, it is interpreted as the
 vector <i>v</i>.

 @param {number} x the <i>x</i> coordinate to subtract.
 @param {number} y the <i>y</i> coordinate to subtract.
 @returns {pv.Vector} a new vector.