# E4000

Generic type variable name is already used.

## Erroneous example

```{literalinclude} /sources/error_codes/4000_error/top.mbt
:language: moonbit
```

## Suggestion

Use different names for type variables:

```{literalinclude} /sources/error_codes/4000_fixed/top.mbt
:language: moonbit
```

Or remove the duplicate type parameter if you meant to use the same type:

```{literalinclude} /sources/error_codes/4000_fixed/top_1.mbt
:language: moonbit
```