     // MARK: - GraphableEquation
     
     var drawingColor: UIColor = UIColor.black
-    var inputDomain: Range<CGFloat>?
+    var domain: Range<CGFloat>?
     
     // MARK: - Equation
-    
-    func compute(withInterval interval: CGFloat, between x1: CGFloat, and x2: CGFloat) -> [Coordinate]
-    {
-        var coordinates : [Coordinate] = []
-        
-        for x in stride(from: x1, through: x2, by: interval)
-        {
-            coordinates.append(Coordinate(x: x, y:  self.compute(at: x)))
-        }
-        
-        return coordinates
-    }
     
     func compute(at x: CGFloat) -> CGFloat
     {

    func drawEquation(_ equation: GraphableEquation, withContext context: CGContext, inRect rect: CGRect, at x: CGFloat)
    {
        let previousX = x - self.interval
        var rangeContainsPreviousX = false
        
        if let range = equation.inputDomain
        {
            rangeContainsPreviousX = range.contains(previousX)
            

    let graph = GraphView(withSmallerXBound: -15.0, largerXBound: 15.0, andInterval: 0.5)
    
    let line = Line(slope: 0.5, offset: 0)
//    let sine = Sine()
    
    graph.addEquation(line)
    //    graph.addEquation(sine)
    //: You can add these yourself.
    
    let cosine = Cosine(period: 1.0, amplitude: 1.0, phaseShift: -1.0, verticalShift: 0.0)
    cosine.drawingColor = UIColor(red: 1.0, green: 0.2, blue: 0.2, alpha: 1.0)
    cosine.domain = Range(uncheckedBounds: (lower: 0.0, upper: 8.0))
    
    graph.addEquation(cosine)
    
