diff --git a/packages/core/src/parser/conditions.ts b/packages/core/src/parser/conditions.ts
index 85d7be51..c9258d36 100644
--- a/packages/core/src/parser/conditions.ts
+++ b/packages/core/src/parser/conditions.ts
@@ -367,6 +367,19 @@ export abstract class BaseConditionParser {
       }
       return streams.length;
     };
+
+    this.parser.functions.not = function (
+      streams: ParsedStream[],
+      originalStreams: ParsedStream[]
+    ) {
+      if (!Array.isArray(originalStreams)) {
+        throw new Error(
+          "Please use one of 'totalStreams' or 'previousStreams' as the second argument"
+        );
+      }
+      const streamIds = new Set(streams.map((stream) => stream.id));
+      return originalStreams.filter((stream) => !streamIds.has(stream.id));
+    };
   }
 
   protected async evaluateCondition(condition: string): Promise<any> {