Write the systematic IUPAC names of the following compounds :
`HOOC - CH = CH - COOH`

Explanation

To write the systematic IUPAC name for the compound `HOOC - CH = CH - COOH`, we will follow these steps:

### Step 1: Identify the longest carbon chain
The compound has a total of 4 carbon atoms. The longest chain consists of these 4 carbon atoms.

### Step 2: Number the carbon chain
We will number the carbon chain starting from the end nearest to the carboxylic acid group (–COOH) to give the substituents the lowest possible numbers. The numbering will be as follows:
1. Carboxylic acid (C1)
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