Two Channels, One Groove—How Do Stereo Vinyl Records Do It?

Not only do stereophonic vinyl records pack two audio channels into one groove, they encode it in such a way that if a stereo record is played on a mono turntable, both channels are correctly mixed together into the single speaker. Playing a mono record on a stereo turntable plays the single channel through both stereo speakers. All of this is done without any fancy electronics or signal processing. But how?