4. **Development Status:**

"Blind Merge Mining":

Seemed more like a theoretical idea without widespread

implementations as of my knowledge cutoff (September 2021).

"Relay Validation" in Polkadot:

It's an implemented and operational concept within the Polkadot network.

In summary, "blind merge mining" appears to be a term

that can refer to various theoretical concepts of hash

sharing between blockchains, whereas "relay validation"

in Polkadot is a concrete and implemented approach that

allows main chain validators to validate transactions on parachains.