Andrx may have the best shot at winning the court battle because it claims to have developed a patented two-layer formulation that completely avoids Astra's middle layer.

FORBES: Hard to Swallow

The hybrid disc works by making the Blu-ray layer act like a two way mirror, reflecting enough light for Blu-ray playback, but letting enough light through for HD DVD operation.

ENGADGET: Three's company: Warner patents all-in-one hybrid disc HD

Gmail offers a two-step verification to add an extra layer of security.

CNN: Bush email hacking a wake up call

Critics of Twitter say the service is vulnerable to unauthorized messages because the company hasn't widely implemented "two-factor authentication, " an extra layer of protection to ensure a person who enters a password to a digital service is the authorized user.

WSJ: False Associated Press Twitter Message Sparks Stock-Market Selloff

While it's easy to see how TouchPad and smartphone sales would symbiotically attract developers, it's less clear how much apps for those products would have in common with, say, those on a printer front panel or on a layer living on top of Windows on a PC -- two possibilities that HP has raised for device markets where it is particularly strong.

ENGADGET: Switched On: webOS wherever

We had two six-wheeler trucks, too, but it was warmer in the buggy: you have an extra layer of clothing and a full-face helmet.

BBC: Polar express

To enable this material to store electrical energy, two layers of woven fibres are made into a sandwich, separated by a thin layer of a glass-based insulating material.

ECONOMIST: Carbon-composite batteries

Bed-nesters looking for support have two options: Place the bolster on the mattress right against the headboard and layer on regular pillows to create a slanted wedge, ideal for watching TV.

WSJ: Bolster Cushions Win Best Supporting Rolls