In its amiable, quiet, PG-13 way, "The Invention of Lying" is a remarkably radical comedy. It opens with a series of funny, relentlessly logical episodes in a world where everyone always tells the truth, and then slips in the implication that religion is possible only in a world that has the ability to lie. Then it wraps all of this into a sweet love story. Ricky Gervais plays a pudgy everyman named Mark, who's a writer for a company that produces movies of stunning tedium.