Disclosed is a valve being attached to a fuel tank, the valve permitting a vaporized fuel to flow out and inhibiting a liquid fuel from flowing out. The amplifier systems use a differential first stage and a second stage of two pair of nested current mirrors interconnected in a particular way. In another embodiment, a user is provided with content that he is not allowed to access but is allowed to access a preview version of the content by creating a license that specifies the user’s access to the preview content, wherein the license is stored on a memory device that stores the preview content. Moreover, the method includes if the second resolution is finer than the first resolution, selecting a third resolution from the plurality of predetermined resolutions, obtaining a second geometry representation associated with the third resolution, generating a third geometry representation, and determining whether the ray and the first surface patch intersect.