TraditionalForm[expr] prints as an approximation to the traditional mathematical notation for expr.

Mathematica provides a compact way of representing boxes in terms of strings. This is particularly convenient when you want to import or export specifications of boxes as ...

CirclePlus[x, y, ...] displays as x\[CirclePlus]y\[CirclePlus]....

Null is a symbol used to indicate the absence of an expression or a result. It is not displayed in ordinary output. When Null appears as a complete output expression, no ...

Superscript[x, y] is an object that formats as x^y.

Converting to and from character codes. Mathematica assigns every character that can appear in a string a unique character code. This code is used internally as a way to ...

Characters["string"] gives a list of the characters in a string.

When you enter a piece of input such as 2+2, Mathematica first recognizes the + as an operator and constructs the expression Plus[2,2], then uses the built-in rules for Plus ...

OverscriptBox[x, y] is the low-level box representation for OverscriptBox[x, y] in notebook expressions.

expr[[i]] or Part[expr, i] gives the i\[Null]^th part of expr. expr[[-i]] counts from the end. expr[[i, j, ...]] or Part[expr, i, j, ...] is equivalent to expr[[i]][[j]] .... ...