Add to ORKGSecurities markets theory includes repo and distinguishes shorting from issuing. Here we revisit whether trading alone can give rise to Ponzi schemes and rational bubbles. We show that under the same institutional arrangements that limit re-hypothecation (e.g., through segregated haircut rules or explicit leverage constraints on haircut collecting dealers), (1) trading Ponzi schemes are prevented without having to assume uniform impatience, (2) for securities in positive net supply, bubbles are ruled out under complete markets but may occur when markets are incomplete. We give an example of such a bubble, under a finite present value of wealth.Repo, short sale, bubble, repo specialness, Ponzi scheme, leverage, trading.