diff --git a/eslint.config.mjs b/eslint.config.mjs
index 104ad06..2ad2b68 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -38,8 +38,9 @@ export default tseslint.config(
 
       "@typescript-eslint/consistent-type-imports": "error",
       "@typescript-eslint/explicit-module-boundary-types": "error",
-      "@typescript-eslint/restrict-template-expressions": ["error", { allowNumber: true }],
       "@typescript-eslint/no-explicit-any": "error",
+      "@typescript-eslint/no-unnecessary-condition": ["error", { allowConstantLoopConditions: true }],
+      "@typescript-eslint/restrict-template-expressions": ["error", { allowNumber: true }],
       "@typescript-eslint/no-unused-vars": [
         "warn",
         { args: "all", argsIgnorePattern: "^_.*", varsIgnorePattern: "^_.*" },
@@ -60,12 +61,13 @@ export default tseslint.config(
   // -------------------------------
   {
     rules: {
+      //"@typescript-eslint/consistent-type-definitions": "off",
       //"@typescript-eslint/no-empty-function": "off",
       //"@typescript-eslint/no-inferrable-types": "off",
       "@typescript-eslint/no-non-null-assertion": "off",
-      //"no-constant-condition": "off",
-      //"@typescript-eslint/consistent-type-definitions": "off",
+      "@typescript-eslint/unified-signatures": "off",
       //"@typescript-eslint/use-unknown-in-catch-callback-variable": "off",
+      //"no-constant-condition": "off",
     },
   },
 
diff --git a/src/builtins.ts b/src/builtins.ts
index 912e266..a9ac194 100644
--- a/src/builtins.ts
+++ b/src/builtins.ts
@@ -11,7 +11,7 @@ export function find<T>(iterable: Iterable<T>, predicate?: Predicate<T>): T | un
   const it = iter(iterable);
   if (predicate === undefined) {
     const value = it.next();
-    return value.done ? value.value : value.value;
+    return value.done ? undefined : value.value;
   } else {
     let res: IteratorResult<T>;
     let i = 0;
@@ -215,7 +215,6 @@ function range_(start: number, stop: number, step: number): IterableIterator<num
  * The produced range will be empty if the first value to produce already does
  * not meet the value constraint.
  */
-
 export function range(stop: number): IterableIterator<number>;
 export function range(start: number, stop: number, step?: number): IterableIterator<number>;
 export function range(startOrStop: number, definitelyStop?: number, step = 1): IterableIterator<number> {
diff --git a/src/custom.ts b/src/custom.ts
index b1c5a30..b21e045 100644
--- a/src/custom.ts
+++ b/src/custom.ts
@@ -7,7 +7,7 @@ function isNullish<T>(x: T): x is NonNullable<T> {
   return x != null;
 }
 
-function isDefined<T>(x: T): boolean {
+function isDefined(x: unknown): boolean {
   return x !== undefined;
 }
 
diff --git a/src/itertools.ts b/src/itertools.ts
index 31c7bc8..be161bc 100644
--- a/src/itertools.ts
+++ b/src/itertools.ts
@@ -345,7 +345,7 @@ export function* izipMany<T>(...iters: Iterable<T>[]): IterableIterator<T[]> {
 export function* permutations<T>(iterable: Iterable<T>, r?: number): IterableIterator<T[]> {
   const pool = Array.from(iterable);
   const n = pool.length;
-  const x = r === undefined ? n : r;
+  const x = r ?? n;
 
   if (x > n) {
     return;
diff --git a/src/more-itertools.ts b/src/more-itertools.ts
index c2c4e4c..e68520a 100644
--- a/src/more-itertools.ts
+++ b/src/more-itertools.ts
@@ -1,4 +1,4 @@
-import { enumerate, iter, map } from "./builtins";
+import { iter, map } from "./builtins";
 import { izip, repeat } from "./itertools";
 import type { Predicate, Primitive } from "./types";
 import { primitiveIdentity } from "./utils";