Based on prior knowledge, the safety of a car is an important factor when determining the decision to buy a car. In general, a car with higher safety ratings would be more likely to receive a higher rating for the decision to buy.

Here is the analysis of the relationship between the feature "safety" and the target variable "decision to buy":

- Unacceptable: In this case, it is likely that the safety rating of the car is low or medium. Therefore, the possible values of the "safety" feature for the target class "unacceptable" are ['low', 'med'].

- Acceptable: If the decision to buy the car is rated as "acceptable", it is possible that the safety rating of the car is medium or high. Therefore, the possible values of the "safety" feature for the target class "acceptable" are ['med', 'high'].

- Good: For a decision classed as "good", the safety rating of the car is likely to be high. Therefore, the possible value of the "safety" feature for the target class "good" is ['high'].

- Very Good: A car with a very good safety rating would likely receive a rating of "very good" for the decision to buy. Therefore, the possible value of the "safety" feature for the target class "very good" is ['high'].

Based on this analysis, here is the dictionary:

```json
{
	"unacceptable": ["low", "med"],
	"acceptable": ["med", "high"],
	"very good": ["high"],
	"good": ["high"]
}
```