# AUR0108

## Error Message

`AUR0108: Ast eval error: unknown binary operator: "{{op}}"`

## Description

This error occurs when Aurelia encounters a binary operator it does not support while evaluating an expression.

## Solution

* Use supported operators, or move complex logic into a view-model method.

## More Information

This code is also documented under the runtime-html section: [AUR0108](https://docs.aurelia.io/developer-guides/error-messages/runtime-html/aur0108).