1 files changed, 69 insertions, 0 deletions

diff --git a/subprojects/logic/src/main/java/tools/refinery/logic/literal/BooleanLiteral.java b/subprojects/logic/src/main/java/tools/refinery/logic/literal/BooleanLiteral.java
new file mode 100644
index 00000000..fd1dbf91
--- /dev/null
+++ b/subprojects/logic/src/main/java/tools/refinery/logic/literal/BooleanLiteral.java
@@ -0,0 +1,69 @@
+/*
+ * SPDX-FileCopyrightText: 2021-2023 The Refinery Authors <https://refinery.tools/>
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package tools.refinery.logic.literal;
+
+import tools.refinery.logic.equality.LiteralEqualityHelper;
+import tools.refinery.logic.equality.LiteralHashCodeHelper;
+import tools.refinery.logic.substitution.Substitution;
+import tools.refinery.logic.term.Variable;
+
+import java.util.Set;
+
+public enum BooleanLiteral implements CanNegate<BooleanLiteral> {
+        TRUE(true),
+        FALSE(false);
+
+        private final boolean value;
+
+        BooleanLiteral(boolean value) {
+                this.value = value;
+        }
+
+        @Override
+        public Set<Variable> getOutputVariables() {
+                return Set.of();
+        }
+
+        @Override
+        public Set<Variable> getInputVariables(Set<? extends Variable> positiveVariablesInClause) {
+                return Set.of();
+        }
+
+        @Override
+        public Set<Variable> getPrivateVariables(Set<? extends Variable> positiveVariablesInClause) {
+                return Set.of();
+        }
+
+        @Override
+        public Literal substitute(Substitution substitution) {
+                // No variables to substitute.
+                return this;
+        }
+
+        @Override
+        public BooleanLiteral negate() {
+                return fromBoolean(!value);
+        }
+
+        @Override
+        public boolean equalsWithSubstitution(LiteralEqualityHelper helper, Literal other) {
+                return equals(other);
+        }
+
+        @Override
+        public int hashCodeWithSubstitution(LiteralHashCodeHelper helper) {
+                return hashCode();
+        }
+
+        @Override
+        public String toString() {
+                return Boolean.toString(value);
+        }
+
+        public static BooleanLiteral fromBoolean(boolean value) {
+                return value ? TRUE : FALSE;
+        }
+}