Reduction of copper (1) oxide with copper (1) sulphide.

Explanation

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Copper (I) oxide is represented as Cu2O, where copper is in the +1 oxidation state.
- Copper (I) sulfide is represented as Cu2S, where copper is also in the +1 oxidation state.

2. **Understand the Reaction Type**:
- The reaction between Cu2O and Cu2S is known as auto-reduction. This occurs when one compound reduces another while being oxidized itself.
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