# Part 3.4HTML entities

## What a HTML entity is

HTML entities refer to specific HTML codes that are used to create platform independent characters. Such characters include characters such as & and ". These characters are used in special ways on the web such as in URLs for instance: test.co.uk/?a=1&amp;b=1.

These characters can also be used in HTML documents such as this one to represent specialised characters, for instance, such as mathematical symbols such as some formal logic displayed below:

HTML
&forall;x, y : N | x &lt; y &bull; x &isin; COLLECTION &and; x &notin; REALS

∀x, y : N | x < y • x ∈ COLLECTION ∧ x ∉ REALS

HTML is getting more equipped with Latex characters such as those above. They may however not display in all browsers. There are some general every day and more useful characters such as the ampersand symbol (&) and the pound sign (£). Some characters can even be given special symbols above them such as a grave or acute such as this j character: j̀ or this q́.

## List of HTML entities

The table below shows a few of the entities that exist out there that can actually be very useful. The list is very broad as well.

EntityCodeName
&&amp;Ampersand. This is an example of an escaped character because the ampersand is used to open a HTML entity.
<&lt;Less than. This is an example escaped character because in HTML the < > characters enclose a tag.
>&gt;Greater than. This is an example escaped character because in HTML the < > characters enclose a tag.
&le;Less than or equal to.
&ge;Greater than or equal to.
£&pound;Pound sign
¥&yen;Japanese Yen sign
®&reg;Registered symbol
&cup;Cup or Union symbol
&cap;Cap or Intersection symbol
&forall;For all, the universal quantifier
&exist;There exists, existential quantifier
&alefsym;Aleph naught.
&equiv;Identically equal to
Δ&Delta;Delta, representing a change in some variable (note the capital D because this is the capitalised version)
Ξ&Xi;Xi, representing a variable that remains constant (note the capital X because this is the capitalised version)
&empty;Empty, used for representing empty sets.
π&pi;Pi
&rArr;Right arrow, used for logical implication, A ⇒ B = ¬A ∨ B
¬&not;Negation or not. Can be used to negate some Boolean logic.
&and;Logical and, sometimes known as l-and.
&or;Logical or, sometimes known as l-or.
&oplus;XOR - exclusive or, true when only one of the values is true. A ⊕ B
&sum;The sum of n values. a1 + a2 + a3 + ... an
&isin;Is an element of.
&notin;Is not an element of.
&sub;Is a subset of.
Ω&Omega;Omega
&infin;Infinity
&int;An integral
×&times;Multiplication
÷&divide;Division
&bull;Bullet. Great for formal logic.
&hArr;Logically equivelant.
&para;Paragraph marker.
&real;The set of real numbers (such as 1.0, 1.1, 1.2...)
θ&theta;Theta.

And that's how HTML is used to store symbols.

## Alternative entities

HTML can represent others using hexadecimal such as the cube root symbol: ∛ and ∜. Mentioned above was the option of adding a grave or acute to a character. It was also done with hexadecimal. These are called hex entities. They are more expansive but more difficult to learn. Not only that, but they have no system of order and are also limited, for instance there is no cube root of 5 symbol.

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