Things I keep having to look up again.

1. Warrants. Issued by the company itself rather than written by a third party, so exercise creates new shares and the strike proceeds go to the firm. That is the whole difference from a call option, and it is why exercise dilutes: with N shares and M warrants outstanding, the warrant is worth N/(N+M) times an otherwise identical call, and the volatility that belongs in that call is asset volatility, not the equity volatility you can observe. They run two to ten years rather than months, often ride along with a bond issue as a sweetener for a lower coupon, and in SPACs arrive as a fraction of a unit struck at $11.50 against a $10 trust, redeemable by the sponsor at $0.01 once the stock clears $18.