Repository: TypeScript
Issue: `Exclude<Exclude<T, null>, undefined>` is not assignable to `Exclude<T, null | undefined>` and vice versa
Labels: Suggestion,Needs Proposal

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**TypeScript Version:**  Nightly

<!-- Search terms you tried before logging this (so others can find this issue more easily) -->
**Search Terms:**
typescript nullness inference

**Expected behavior:**
They should be assignable to each other.

**Actual behavior:**
They are not considered assignable to each other.
```
Type 'Exclude<Exclude<T, null>, undefined>' is not assignable to type 'Exclude<T, null | undefined>'.
  Type 'Exclude<T, null>' is not assignable to type 'Exclude<T, null | undefined>'.
    Type 'T' is not assignable to type 'Exclude<T, null | undefined>'.(2322)
```
and
```
Type 'Exclude<T, null | undefined>' is not assignable to type 'Exclude<Exclude<T, null>, undefined>'.
  Type 'T' is not assignable to type 'Exclude<Exclude<T, null>, undefined>'.(2322)
```

<!-- Did you find other bugs that looked similar? -->
**Related Issues:**
N/A

**Code**
```ts
export function f<T>(v: Exclude<Exclude<T, null>, undefined>) {
    const w: Exclude<T, null | undefined> = v;
}

export function g<T>(v: Exclude<T, null | undefined>) {
    const w: Exclude<Exclude<T, null>, undefined> = v;
}

```



<details><summary><b>Output</b></summary>

```ts
export function f(v) {
    const w = v;
}
export function g(v) {
    const w = v;
}

```


</details>


<details><summary><b>Compiler Options</b></summary>

```json
{
  "compilerOptions": {
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "strictBindCallApply": true,
    "noImplicitThis": true,
    "noImplicitReturns": true,
    "useDefineForClassFields": false,
    "alwaysStrict": true,
    "allowUnreachableCode": false,
    "allowUnusedLabels": false,
    "downlevelIteration": false,
    "noEmitHelpers": false,
    "noLib": false,
    "noStrictGenericChecks": false,
    "noUnusedLocals": false,
    "noUnusedParameters": false,
    "esModuleInterop": true,
    "preserveConstEnums": false,
    "removeComments": false,
    "skipLibCheck": false,
    "checkJs": false,
    "allowJs": false,
    "declaration": true,
    "experimentalDecorators": false,
    "emitDecoratorMetadata": false,
    "target": "ES2017",
    "module": "ESNext"
  }
}
```


</details>

**Playground Link:** [Provided](https://www.typescriptlang.org/play/?ts=3.9.0-dev.20200422&ssl=4&ssc=1&pln=1&pc=1#code/KYDwDg9gTgLgBAMwK4DsDGMCWEWIDwAqAfABQBuAXHAKIhoA2SAJsHrQ86wQDRwpL16RXqhYJMKYEyIBKOAG8AUHBVw0OAM7wA7lXaMWhXv0FwAPnFHBxk6XAC8cMgG5FAX0WLQkWIlQZsXABzQlJKGjoDLmMBenNLFDEJKVkFZVV1FC04XQiOQ31OIz5Y4QSk2yIHJ1cPRSA)