diff --git a/index.d.ts b/index.d.ts
index 591058a..f4e7432 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -232,6 +232,19 @@ declare namespace R {
 
     interface Static {
 
+       /**
+        * A special placeholder value used to specify "gaps" within curried
+        * functions, allowing partial application of any combination of
+        * arguments, regardless of their positions.
+        * NOTE: can't type this yet, for binary functions consider R.flip!
+        */
+       __: any; // { "@@functional/placeholder": boolean };
+       // ^ don't type by value, since it can be inserted anywhere...
+       // Note this is still not useful, as it doesn't take into account how it changes formulas (leaving holes!).
+       // This remains TODO, and should be done on the level of curried functions, but that
+       // pretty much requires being able to express the separate functions as a single curried function...
+       // until that moment handling this would mean having to handle each possible combination for each function. :(
+
        /**
         * Adds two numbers. Equivalent to a + b but curried.
         */