I'm struggling to understand the difference between Actor-Critic and Advantage Actor-Critic.
At least I know they are different from Asynchronous Advantage Actor-Critic (A3C), as A3C adds asynchronous mechanism that uses multiple worker agents interacting with their own copy of environment and report the gradient to the global agent.
But what is the difference from the Actor-Critic and Advantage Actor-Critic (A2C)? Is it simply with or without Advantage function? But then, does the Actor-Critic have any other implementation except the use of Advantage function?
Or maybe are they synonyms and Actor-Critic is just a shorthand for A2C?