1 files changed, 15 insertions, 2 deletions

diff --git a/subprojects/store/src/main/java/tools/refinery/store/representation/TruthValue.java b/subprojects/store/src/main/java/tools/refinery/store/representation/TruthValue.java
index 40baf9a5..f81ee9a4 100644
--- a/subprojects/store/src/main/java/tools/refinery/store/representation/TruthValue.java
+++ b/subprojects/store/src/main/java/tools/refinery/store/representation/TruthValue.java
@@ -36,6 +36,10 @@ public enum TruthValue {
                 return this != UNKNOWN;
         }
 
+        public boolean isConcrete() {
+                return this == TRUE || this == FALSE;
+        }
+
         public boolean must() {
                 return this == TRUE || this == ERROR;
         }
@@ -55,9 +59,18 @@ public enum TruthValue {
         public TruthValue merge(TruthValue other) {
                 return switch (this) {
                         case TRUE -> other == UNKNOWN || other == TRUE ? TRUE : ERROR;
-                        case FALSE -> other == TruthValue.UNKNOWN || other == TruthValue.FALSE ? FALSE : ERROR;
+                        case FALSE -> other == UNKNOWN || other == FALSE ? FALSE : ERROR;
                         case UNKNOWN -> other;
-                        default -> ERROR;
+                        case ERROR -> ERROR;
+                };
+        }
+
+        public TruthValue join(TruthValue other) {
+                return switch (this) {
+                        case TRUE -> other == ERROR || other == TRUE ? TRUE : UNKNOWN;
+                        case FALSE -> other == ERROR || other == FALSE ? FALSE : UNKNOWN;
+                        case UNKNOWN -> UNKNOWN;
+                        case ERROR -> other;
                 };
         }
 }