diff --git a/src/ops/choose.mjs b/src/ops/choose.mjs
index c285dc7..dd22dc2 100644
--- a/src/ops/choose.mjs
+++ b/src/ops/choose.mjs
@@ -1,11 +1,13 @@
-/* Note this is not a good algorithm for computing binomial coefficients,
+import Returns from '../core/Returns.mjs'
+
+/* Note this is _not_ a good algorithm for computing binomial coefficients,
  * it's just for demonstration purposes
  */
 export const choose = {
-   'NumInt,NumInt': ({factorial}) => (n,k) => Number(
-      factorial(n) / (factorial(k)*factorial(n-k))),
+   'NumInt,NumInt': ({factorial}) => Returns(
+      'NumInt', (n,k) => Number(factorial(n) / (factorial(k)*factorial(n-k)))),
    'bigint,bigint': ({
       factorial
-   }) => (n,k) => factorial(n) / (factorial(k)*factorial(n-k))
+   }) => Returns('bigint', (n,k) => factorial(n) / (factorial(k)*factorial(n-k)))
 }
         
diff --git a/src/ops/factorial.mjs b/src/ops/factorial.mjs
index bb07047..b1154f3 100644
--- a/src/ops/factorial.mjs
+++ b/src/ops/factorial.mjs
@@ -1,8 +1,15 @@
-export function factorial(n) {
+import Returns from '../core/Returns.mjs'
+
+/* Plain functions are OK, too, and they can be decorated with a return type
+ * just like an implementation.
+ */
+const factorial = Returns('bigint', function factorial(n) {
    n = BigInt(n)
    let prod = 1n
    for (let i = n; i > 1n; --i) {
       prod *= i
    }
    return prod
-}
+})
+
+export {factorial}
diff --git a/src/ops/floor.mjs b/src/ops/floor.mjs
index 2fbe106..3754dcb 100644
--- a/src/ops/floor.mjs
+++ b/src/ops/floor.mjs
@@ -25,7 +25,6 @@ export const floor = {
 
    // OK to include a type totally not in Pocomath yet, it'll never be
    // activated.
-   // Fraction: ({quotient}) => f => quotient(f.n, f.d), // oops have that now
    BigNumber: ({
       'round(BigNumber)': rnd,
       'equal(BigNumber,BigNumber)': eq
diff --git a/test/_pocomath.mjs b/test/_pocomath.mjs
index 5d80e85..c4a5c28 100644
--- a/test/_pocomath.mjs
+++ b/test/_pocomath.mjs
@@ -63,6 +63,8 @@ describe('The default full pocomath instance "math"', () => {
       assert.strictEqual(math.returnTypeOf('isZero', 'NumInt'), 'boolean')
       assert.strictEqual(
          math.returnTypeOf('roundquotient', 'NumInt,number'), 'NumInt')
+      assert.strictEqual(
+         math.returnTypeOf('factorial', 'NumInt'), 'bigint')
    })
 
    it('can subtract numbers', () => {