<p><b>Matchbox Theatre</b> presents a sketch show in miniature: thirty short entertainments by Michael Frayn, author of <i>Skios</i> and <i>Noises Off</i>, ''the funniest farce ever written'' (<i>New York Times</i>).<br><br>These tiny plays are offered here for performance in the smallest theatre in the world: the theatre of your own imagination. The scripts are provided. Everything else -- casting, set design, ice-cream sales -- is up to you . . .</p>