You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mod.rs
    path of file: ./repos/snarkVM/ledger/block/src/header/metadata
    
    the code of the file until where you have to start completion: // Copyright (C) 2019-2023 Aleo Systems Inc.
// This file is part of the snarkVM library.

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at:
// http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

mod bytes;
mod genesis;
mod serialize;
mod string;
mod to_bit
    
    pub fn is_valid(&self) -> bool {
        match self.height == 0u32 {
            true => self.is_genesis(),
            false => {
                // Ensure the network ID is correct.
                self.network == N::ID
                    // Ensure the round is nonzero.
                    && self.round != 0u64
                    // Ensure the height is nonzero.
                    && self.height != 0u32
                    // Ensure the round is at least as large as the height.
                    && self.round >= self.height as u64
                    // Ensure the coinbase target is at or above the minimum.
                    && self.coinbase_target >= N::GENESIS_COINBASE_TARGET
                    // Ensure the proof target is at or above the minimum.
                    && self.proof_target >= N::GENESIS_PROOF_TARGET
                    // Ensure the coinbase target is larger than the proof target.
                    && self.coinbase_target > self.proof_target
                    // Ensure the last coinbase target is at or above the minimum.
                    && self.last_coinbase_target >= N::GENESIS_COINBASE_TARGET
                    // Ensure the last coinbase timestamp is after the genesis timestamp.
                    && self.last_coinbase_timestamp >= N::GENESIS_TIMESTAMP
                    // Ensure the timestamp in the block is after the genesis timestamp.
                    && self.timestamp > N::GENESIS_TIMESTAMP
            }
        }
    }