1, positive example:

Positive example, also known as "positive example", is an appropriate example or illustration of a concept. For example, elephants, lions, whales and dolphins are all positive examples of the concept of mammals, and these positive examples all contain common essential characteristics.

2. Counterexample:

Counterexample, also known as counterexample, refers to an example that does not contain or only contains a small part of the main attributes and key features of a concept or rule. Positive case analysis can explain the key features of the concept in detail, and counterexample analysis can eliminate the interference of irrelevant features.

3. Variants:

Meaning one refers to a form of expression formed by changing the non-essential characteristics of an object to highlight the essential characteristics of the object;

The second meaning refers to highlighting the non-essential characteristics of an object by changing the essential characteristics of the object, thus changing the connotation of the concept of display.

In short, variation refers to the change of irrelevant characteristics of the positive example of a concept or rule. Elephants and whales, for example, have the common characteristics of viviparous and lactation, but they are different in unrelated characteristics, one is on land and the other is in the ocean. Penguin, dinosaur and snake are counterexamples of the concept of mammals, and they do not have the characteristics of viviparous and lactation. In fact, the counterexample of the concept and its positive example may have the same irrelevant characteristics, but they do not have the common essential characteristics of the positive example.

Examples of differences:

Let's take the concept of "bird" as an example. It is generally believed that the essential characteristics of birds include: sharp beak, feathers, egg laying and so on. Non-essential features include: small head, flying, etc. So to sum up:

Positive example: there are essential features and irrelevant features (swallows, sparrows, etc. ).

Counterexample: There are few/no essential features, and most of them are irrelevant features (cockroaches, bats, etc. ).

Variant: has essential characteristics, but has nothing to do with change (penguin, ostrich, etc. ).