use `exists` instead of `put`

cozo-core/src/query/stored.rs

@@ -255,8 +255,7 @@ impl<'a> SessionTx<'a> {
                             .try_collect()?,
                     );
                     let key = relation_store.adhoc_encode_key(&extracted, *span)?;
-                    let existing = self.tx.get(&key, true)?;
+                    if self.tx.exists(&key, true)? {
-                    if existing.is_some() {
                         bail!(TransactAssertionFailure {
                             relation: relation_store.name.to_string(),
                             key: extracted.0,

cozo-lib-c/cozo_c.h

@@ -1,8 +1,4 @@
-// Copyright 2022, The Cozo Project Authors.
+/* Copyright 2022, The Cozo Project Authors. Licensed under MIT/Apache-2.0/BSD-3-Clause. */
-//
-// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
-// If a copy of the MPL was not distributed with this file,
-// You can obtain one at https://mozilla.org/MPL/2.0/.
 
 #ifndef COZO_C_H
 #define COZO_C_H