Double trigger acceleration, as you might have surmised after reading “accelerating vesting”, requires two conditions for accelerated vesting. Double trigger acceleration was designed to fundamentally protect employees from being terminated when the value of the employee’s unvested equity into the employee is greater than the cost of replacement in the event of an acquisition.
Cooley Go's Pulling the Trigger(s): What is Double-Trigger Acceleration and How Does it Work? at cooleygo
Nicholas Carlson's What is a Double Trigger? at Business Insider
Raad Ahmed's The Difference Between Single Trigger and Double Trigger Acceleration Of Vesting During An Acquisition at raadahmed
Joe Wallin's Single & Double Trigger Acceleration at Startup Law Blog
Dan Shapiro's Vesting is a hack at danshapiro
Jonathan D. Grworek's Double Trigger Acceleration at Morse Barnes-Brown Pendleton