     func isNegative() -> Bool {
         return !isPositive()
     }
-
-    func isZero() -> Bool {
-        return self == 0
-    }
+    
+    // MARK: - Instance Methods
     
     func split() -> [Int] {
         var result = [Int]()

        return self.seconds
    }
    
    func isEven() -> Bool {
        return (self % 2) == 0
    }

import Foundation

public extension Int {
    
    // MARK: - Properties
    
    var years: NSTimeInterval {
        return 365 * self.days
