Maths for ML / Notation

\equiv

identical to

Arithmetic and relationsIntermediate

Say it “is identically equal to”

Equal for every possible input, or true by definition. Some authors use it to mean 'defined as'.

Example

f(x) \equiv 0

f returns 0 no matter what x is.

Where you’ll see it in ML

Stating that something holds everywhere, e.g. a constant function.

Don’t confuse it with

$\coloneqq$ is defined as Introduces a new name for an expression. It's an assignment, not a claim to check.
$=$ equals Both sides have exactly the same value.

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