Expression Structure (Mathematica Guide)

A foundational idea in Mathematica is that all expressions—whatever they may represent—ultimately have a uniform tree-like structure.

First (Built-in Mathematica Symbol)

First[expr] gives the first element in expr.

Last (Built-in Mathematica Symbol)

Last[expr] gives the last element in expr.

OutputForm (Built-in Mathematica Symbol)

OutputForm[expr] prints as a two-dimensional representation of expr using only keyboard characters.

String (Built-in Mathematica Symbol)

String is the head of a character string " text".

StringTrim (Built-in Mathematica Symbol)

StringTrim["string"] trims whitespace from the beginning and end of " string".StringTrim["string", patt] trims substrings matching patt from the beginning and end.

$PreRead (Built-in Mathematica Symbol)

$PreRead is a global variable whose value, if set, is applied to the text or box form of every input expression before it is fed to Mathematica.

Head (Built-in Mathematica Symbol)

Head[expr] gives the head of expr.

Most (Built-in Mathematica Symbol)

Most[expr] gives expr with the last element removed.

Rational (Built-in Mathematica Symbol)

Rational is the head used for rational numbers.