Use U+2216 SET MINUS instead of keyboard backslash

[abcdsen-create]

Priority: High

Description

Add
guidance that set difference must use U+2216 SET MINUS (∖) inside MathML, not
U+005C REVERSE SOLIDUS (\). The characters look similar, but the keyboard
backslash is correctly interpreted literally as “backslash.”

Recommended markup

<math
xmlns="http://www.w3.org/1998/Math/MathML">

<mi>A</mi><mo>∖</mo><mi>B</mi>

</math>

Acceptance criteria

• U+2216 and U+005C are distinguished by character name and code point.
• Set difference is encoded inside MathML.
• Production QA flags U+005C within probable set expressions.
• The example is verified to read as “A set minus B,” or the language-appropriate equivalent.