> Aztec.nr API reference, v6.0.0 (mainnet and testnet). Index: https://docs.aztec.network/aztec-nr-api/v6.0.0/llms.txt

# Function get_block_hash_membership_witness

Module: `noir_aztec::oracle::get_membership_witness`

```rust
pub unconstrained fn get_block_hash_membership_witness(
    anchor_block_header: BlockHeader,
    block_hash: Field,
) -> MembershipWitness<30>
```

Returns a membership witness for a `block_hash` in the archive tree whose root is defined in `anchor_block_header`.