             step = n
         }
 
-        if step < 1 { step = 1 } // Less than 1 results in an infinite loop.
+        if step! < 1 { step = 1 } // Less than 1 results in an infinite loop.
         if n < 1    { n = 0 }    // Allow 0 if user wants [[],[],[]] for some reason.
 
         for i in stride(from: 0, through: count, by: step!) {

        - returns: true if self contains all the items
    */
    public func contains <Element: Equatable> (_ items: Element...) -> Bool {
        return items.all { (item: Element) -> Bool in self.indexOf(item) >= 0 }
    }

    /**

        }

        // Less than 1 results in an infinite loop.
        if step! < 1 {
            step = 1
        }
        
