<p>The referencing of UTxO is decribed in the CIP 31 <a href="https://cips.cardano.org/cips/cip31/" rel="nofollow noreferrer">(1)</a>. There it is stated that</p>
<blockquote>
<p>Referencing an output still requires the output to be presented as
part of the transaction and be unspent, so determinism is preserved.</p>
</blockquote>
<p>So no, referencing already spend outputs is not possible to preserve determinism.</p>
<p>On the topic on how these referenced utxo's will be used see the source <a href="https://github.com/input-output-hk/plutus/blob/3c4067bb96251444c43ad2b17bc19f337c8b47d7/plutus-ledger-api/src/PlutusLedgerApi/V2/Contexts.hs#L77" rel="nofollow noreferrer">(2)</a>.
<a href="https://i.sstatic.net/LC5b0.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/LC5b0.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2022-06-10T12:51:30.077Z
2022-06-10T14:00:24.147Z
2022-06-10T14:00:24.147Z
Fermat
<p>When Vasil HF is here with the new plutus version, can we only reference unspent transaction outputs or even spent ones? Is there some documentation on these newly added functions? Preferably haddock documentation.</p>

<plutus><smart-contract>
Referencing (U)TxO's
# Referencing (U)TxO's

(Asked by: username_0 on 2022-06-08)

When Vasil HF is here with the new plutus version, can we only reference unspent transaction outputs or even spent ones? Is there some documentation on these newly added functions? Preferably haddock documentation.

**Tags:** plutus, smart-contract

---

## 1 answers

### Answer by username_0 on 2022-06-10. Score: 2 | Accepted answer

The referencing of UTxO is decribed in the CIP 31 [(1)](https://cips.cardano.org/cips/cip31/). There it is stated that

> Referencing an output still requires the output to be presented as
> part of the transaction and be unspent, so determinism is preserved.

So no, referencing already spend outputs is not possible to preserve determinism.

On the topic on how these referenced utxo's will be used see the source [(2)](https://github.com/input-output-hk/plutus/blob/3c4067bb96251444c43ad2b17bc19f337c8b47d7/plutus-ledger-api/src/PlutusLedgerApi/V2/Contexts.hs#L77).
[![enter image description here](https://i.sstatic.net/LC5b0.png)](https://i.sstatic.net/LC5b0.png)


---

