diff --git a/.meta.json b/.meta.json
index 026058e..601652e 100644
--- a/.meta.json
+++ b/.meta.json
@@ -14,7 +14,7 @@
     },
     "libraries/DocumentQueries.sysml": {
       "algorithm": "SHA256",
-      "value": "7cad8b83772182db5aa917ed36c19feb2e0796ecd6cfbc3b6b1a4c33729b11a7"
+      "value": "c8f30ccffcc2c98609498c7cef83bbd5fdf74423230591721650bb4d1737f5b0"
     },
     "libraries/IdentityMetadata.sysml": {
       "algorithm": "SHA256",
@@ -69,7 +69,7 @@
       "value": "9e00f049209584092dc8bcb398b736c08e6a39b1db667a8a744de3df72a543bf"
     }
   },
-  "created": "2026-10-29T15:08:48Z",
+  "created": "2026-10-29T15:36:02Z",
   "index": {
     "AnalysisRecords": "libraries/AnalysisRecords.sysml",
     "DiagramLayout": "libraries/DiagramLayout.sysml",
diff --git a/libraries/DocumentQueries.sysml b/libraries/DocumentQueries.sysml
index bcdd3f3..16c956b 100644
--- a/libraries/DocumentQueries.sysml
+++ b/libraries/DocumentQueries.sysml
@@ -423,6 +423,18 @@ library package DocumentQueries {
 		return result : Element[0..*] ordered;
 	}
 
+	/* Differ: one row (key, column of left, column of right) per key value present
+	 * in both left and right whose column cells differ — a keyed value comparison;
+	 * keys on one side only are Except's. A key value carried by two rows on one
+	 * side is a model error. */
+	calc def Differ {
+		in left : Element[0..*] ordered;
+		in right : Element[0..*] ordered;
+		in key : String[1];
+		in column : String[1];
+		return result : Element[0..*] ordered;
+	}
+
 	/* Tree: the source rows arranged as a containment tree in pre-order, each
 	 * row nested under the nearest row containing it — its nearest owner among
 	 * the rows, or the individual whose part it is — at the depth the table