diff --git a/TODO.md b/TODO.md
index bf3a75b..366eaa8 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,5 +1,7 @@
 # system-a
 
+[system-a] `samplingObjective`
+
 # the-book
 
 6: An Apple a Day
diff --git a/src/system-a/gradientDescent.ts b/src/system-a/gradientDescent.ts
index 2fa82e4..a52c260 100644
--- a/src/system-a/gradientDescent.ts
+++ b/src/system-a/gradientDescent.ts
@@ -8,15 +8,13 @@ import {
 } from "./index.js"
 import { mul, sub } from "./toys/index.js"
 
-export type GradientDescentOptions = {
-  revs: number
-  learningRate: number
-}
-
 export function gradientDescent(
   objective: (...ps: Array<Tensor>) => Scalar,
   ps: Array<Tensor>,
-  options: GradientDescentOptions,
+  options: {
+    revs: number
+    learningRate: number
+  },
 ): Array<Tensor> {
   const step = gradientDescentStep(objective, options)
   const rs = revise(step, options.revs, ps)
@@ -27,7 +25,10 @@ export function gradientDescent(
 
 export function gradientDescentStep(
   objective: (...ps: Array<Tensor>) => Scalar,
-  options: GradientDescentOptions,
+  options: {
+    revs: number
+    learningRate: number
+  },
 ): (ps: Array<Tensor>) => Array<Tensor> {
   return function step(ps: Array<Tensor>): Array<Tensor> {
     const gs = gradient(objective, ps)
diff --git a/src/system-a/samplingObjective.ts b/src/system-a/samplingObjective.ts
new file mode 100644
index 0000000..36b573c
--- /dev/null
+++ b/src/system-a/samplingObjective.ts
@@ -0,0 +1,17 @@
+import { assertTensorArray, type Tensor } from "./Tensor.js"
+import type { Expectant, Objective } from "./loss.js"
+
+export function samplingObjective(
+  expectant: Expectant,
+  xs: Tensor,
+  ys: Tensor,
+  options: {
+    batchSize: number
+  },
+): Objective {
+  assertTensorArray(xs)
+  const size = xs.length
+  return (...ps) => {
+    throw new Error()
+  }
+}