U+21F8 RIGHTWARDS ARROW WITH VERTICAL STROKE

U+21F8 was added to Unicode in version 3.2 (2002). It belongs to the block Arrows in the Basic Multilingual Plane.

This character is a Math Symbol and is commonly used, that is, in no specific script. The character is also known as z notation partial function.

The glyph is not a composition. It has a Neutral East Asian Width. In bidirectional context it acts as Other Neutral and is not mirrored. In text U+21F8 behaves as Alphabetic regarding line breaks. It has type Other for sentence and Other for word breaks. The Grapheme Cluster Break is Any.

The Wikipedia has the following information about this codepoint:

In mathematics, a partial function from X to Y (written as f: X ↛ Y) is a function f: X′ → Y, for some subset X′ of X. It generalizes the concept of a function f: X → Y by not forcing f to map every element of X to an element of Y (only some subset X′ of X). If X′ = X, then f is called a total function and is equivalent to a function. Partial functions are often used when the exact domain, X′, is not known (e.g. many functions in computability theory).

Specifically, we will say that for any x ∈ X, either:

• f(x) = y ∈ Y (it is defined as a single element in Y) or
• f(x) is undefined.

For example we can consider the square root function restricted to the integers

Thus g(n) is only defined for n that are perfect squares (i.e., 0, 1, 4, 9, 16, ...). So, g(25) = 5, but g(26) is undefined.