Equality misses a near name

Lesson map

Lesson 18. Map, example, EX064.

flowchart TD
  E["d in the set of valid values"] --> Q{"Is the string exactly a member?"}
  Q -->|Yes| H["A hit"]
  Q -->|No| N["Not a hit"]
  N --> L["A near name is not in this mail list"]

The test is equality. This fixture does not contain a near-name row to demonstrate the miss.

Logical drawing

test
  exact membership
in this mail list
  news.example, a different name
  no one-character variant
not in the file
  a similarity score

Learning outcomes

After this chapter, you should be able to:

1. Name the test the hit line uses.
2. Say what this mail list actually uses as a non-match.
3. Refuse a variant the fixture does not contain.

18.1 Exact means the same characters. A lookalike would miss, and this list has none.

The hit test is d in a set of the valid strings. Two strings match only when they are the same sequence of characters. news.example fails because it is a different sequence, not because it is a sneaky variant of donate-elmfield.example. The chapter on limits already says exact matching misses lookalikes. That sentence is a limit of the method. This fixture does not include a lookalike row, so the print cannot be quoted as an example of one. Naming a variant the file never stored would add evidence the run did not produce.

There is no similarity function, no edit-distance, and no "close enough" threshold. A one-character change in a real message would miss for that reason. Sam's notes can say the limit exists. They cannot cite a variant this run did not see. Watching for lookalikes is a separate human task, outside the equality test, and this chapter does not turn that task into a scan of live domains.

vol-12 remains the demonstration of a clean miss that the file does contain. Using it as a stand-in for a lookalike would blur two different failures: a wrong name, and a near name. Only the wrong name is in the list.

Lesson table; scroll horizontally to read all columns →

18.2 Worked example

Lesson table; scroll horizontally to read all columns →

Synthetic case. The miss in the fixture is news.example.

Errors and limits

Do not manufacture a lookalike so the limit has a trophy.

Apply

• EX064 — Equality. What non-match does this mail list actually contain, and may a note add a lookalike domain the file never stored?
  Show marking criteria

  Rubric: 3 = news.example is the stored non-match; the test is exact membership; a lookalike would miss but this list has no such row; do not invent one;; 2 = the stored miss is news.example and no variant is added;; 1 = one domain;; 0 = none.