1 files changed, 71 insertions, 0 deletions

diff --git a/subprojects/logic/src/main/java/tools/refinery/logic/term/NodeVariable.java b/subprojects/logic/src/main/java/tools/refinery/logic/term/NodeVariable.java
new file mode 100644
index 00000000..1a5f2657
--- /dev/null
+++ b/subprojects/logic/src/main/java/tools/refinery/logic/term/NodeVariable.java
@@ -0,0 +1,71 @@
+/*
+ * SPDX-FileCopyrightText: 2021-2023 The Refinery Authors <https://refinery.tools/>
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package tools.refinery.logic.term;
+
+import org.jetbrains.annotations.Nullable;
+import tools.refinery.logic.InvalidQueryException;
+import tools.refinery.logic.literal.ConstantLiteral;
+import tools.refinery.logic.literal.EquivalenceLiteral;
+
+import java.util.Optional;
+
+public final class NodeVariable extends Variable {
+        NodeVariable(@Nullable String name) {
+                super(name);
+        }
+
+        @Override
+        public Optional<Class<?>> tryGetType() {
+                return Optional.empty();
+        }
+
+        @Override
+        public NodeVariable renew(@Nullable String name) {
+                return of(name);
+        }
+
+        @Override
+        public NodeVariable renew() {
+                return renew(getExplicitName());
+        }
+
+        @Override
+        public boolean isNodeVariable() {
+                return true;
+        }
+
+        @Override
+        public boolean isDataVariable() {
+                return false;
+        }
+
+        @Override
+        public NodeVariable asNodeVariable() {
+                return this;
+        }
+
+        @Override
+        public <T> DataVariable<T> asDataVariable(Class<T> type) {
+                throw new InvalidQueryException("%s is a node variable".formatted(this));
+        }
+
+        @Override
+        public int hashCodeWithSubstitution(int sequenceNumber) {
+                return sequenceNumber;
+        }
+
+        public ConstantLiteral isConstant(int value) {
+                return new ConstantLiteral(this, value);
+        }
+
+        public EquivalenceLiteral isEquivalent(NodeVariable other) {
+                return new EquivalenceLiteral(true, this, other);
+        }
+
+        public EquivalenceLiteral notEquivalent(NodeVariable other) {
+                return new EquivalenceLiteral(false, this, other);
+        }
+}