1 files changed, 74 insertions, 0 deletions

diff --git a/subprojects/logic/src/main/java/tools/refinery/logic/term/cardinalityinterval/EmptyCardinalityInterval.java b/subprojects/logic/src/main/java/tools/refinery/logic/term/cardinalityinterval/EmptyCardinalityInterval.java
new file mode 100644
index 00000000..29a7f69d
--- /dev/null
+++ b/subprojects/logic/src/main/java/tools/refinery/logic/term/cardinalityinterval/EmptyCardinalityInterval.java
@@ -0,0 +1,74 @@
+/*
+ * SPDX-FileCopyrightText: 2021-2023 The Refinery Authors <https://refinery.tools/>
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package tools.refinery.logic.term.cardinalityinterval;
+
+import tools.refinery.logic.term.uppercardinality.UpperCardinalities;
+import tools.refinery.logic.term.uppercardinality.UpperCardinality;
+
+// Singleton implementation, because there is only a single empty interval.
+@SuppressWarnings("squid:S6548")
+public final class EmptyCardinalityInterval implements CardinalityInterval {
+        static final EmptyCardinalityInterval INSTANCE = new EmptyCardinalityInterval();
+
+        private EmptyCardinalityInterval() {
+                // Singleton constructor.
+        }
+
+        @Override
+        public int lowerBound() {
+                return 1;
+        }
+
+        @Override
+        public boolean isEmpty() {
+                return true;
+        }
+
+        @Override
+        public UpperCardinality upperBound() {
+                return UpperCardinalities.ZERO;
+        }
+
+        @Override
+        public CardinalityInterval min(CardinalityInterval other) {
+                return this;
+        }
+
+        @Override
+        public CardinalityInterval max(CardinalityInterval other) {
+                return this;
+        }
+
+        @Override
+        public CardinalityInterval add(CardinalityInterval other) {
+                return this;
+        }
+
+        @Override
+        public CardinalityInterval take(int count) {
+                return this;
+        }
+
+        @Override
+        public CardinalityInterval multiply(CardinalityInterval other) {
+                return this;
+        }
+
+        @Override
+        public CardinalityInterval meet(CardinalityInterval other) {
+                return this;
+        }
+
+        @Override
+        public CardinalityInterval join(CardinalityInterval other) {
+                return other;
+        }
+
+        @Override
+        public String toString() {
+                return "error";
+        }
+}