---
categories:
  - Mathematics
tags: [logic]
---

This is also known as _proof by contradiction_. You start with an assumption declared in a subproof. If you can derive a contradiction from this assumption (typically from the introduction of another proposition and its negation), then you are permitted to derive the negation of the auxiliary assumption in the main proof.

[]()![negate-intro 1.png](../img/negate-intro%201.png)