# ULevel::type-mismatch


**Key:** `ULevel::type-mismatch`

**Category:** universe · **Severity:** error

**Source:** [`src/diag/hints.nix:926`](https://github.com/kleisli-io/nix-effects/blob/main/src/diag/hints.nix#L926)

the level argument of `U` must be a Level

## Example

`Hint::ULevel::type-mismatch` means the `ULevel` position supplies a term whose type does not match the expected type. The example shows the failing form first, then one way to give the checker the missing structure.

```nix
# Bad: U expects a Level argument.
u nat

# Better: pass a level.
u level0

```


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