Based on prior knowledge, a thorough analysis of the relationship between the feature "IBS_POST" and the task of determining whether the patient has chronic heart failure can be conducted.

To analyze this relationship, we will examine the distribution of the "IBS_POST" values for patients with and without chronic heart failure. We will compare the proportions of each category within both target classes to understand their relationship.

Let's create a dictionary to summarize the relationship:

```json
{
    "no": ["there was no СHD"],
    "yes": ["exertional angina pectoris", "unstable angina pectoris"]
}
```

Based on the analysis, patients with chronic heart failure are more likely to have "exertional angina pectoris" or "unstable angina pectoris" as their "IBS_POST" values. However, the category "there was no СHD" is associated with the absence of chronic heart failure.

Please note that as per the provided feature categories, the "IBS_POST" values that are hard to predict are not included in the dictionary.