Add/Remove Set CRDT（增减集合CRDT）是否具有单调性？

Let’s break down the key behaviors here in plain terms:

• Internal State Monotonicity: The internal state of an Add/Remove Set CRDT is strictly monotonic. We only ever add elements to its underlying internal collection—there’s no rolling back or removing entries from this layer in logical time. Once an element is added internally, it stays there permanently.
• Observed State Flexibility: Unlike the internal state, the observed state (what end users or dependent systems interact with) supports both element additions and removals. This means the observed state doesn’t need to be monotonic at all—you’ll see elements come and go just like you would with a standard mutable set.
• Chained System Behavior: If you string multiple such CRDT systems together, and implement logic that triggers actions based on whether an element exists or not, the overall behavior loses that obvious monotonicity seen in a single CRDT’s internal state. Operations may appear non-linear or toggle-like, as each system in the chain reacts to the observed state of the previous one.
• Guaranteed Convergence: Even with the non-monotonic observed behavior or the quirks of chained systems, the final state across all replicas will still converge to the same consistent state. This is one of the core guarantees that makes CRDTs reliable for distributed systems.

内容的提问来源于stack exchange，提问作者Drathier