As of Version 6.0, AspectRatioFixed has been superseded by ordinary and Shift interactive resizing of graphics in the front end.
AspectRatio is an option for Graphics and related functions that specifies the ratio of height to width for a plot.
Assert
(Built-in Mathematica Symbol) Assert[test] represents the assertion that test is True. If assertions have been enabled, test is evaluated when the assertion is encountered. If test is not True, then an ...
Assuming[assum, expr] evaluates expr with assum appended to $Assumptions, so that assum is included in the default assumptions used by functions such as Refine, Simplify, and ...
Assumptions is an option for functions such as Simplify, Refine, and Integrate that specifies default assumptions to be made about symbolic quantities.
Asynchronous is an option for WolframAlpha that determines whether to use the asynchronous features of the Wolfram|Alpha API.
AtomQ
(Built-in Mathematica Symbol) AtomQ[expr] yields True if expr is an expression which cannot be divided into subexpressions, and yields False otherwise.
Attributes[symbol] gives the list of attributes for a symbol.
AutoAction is an option for objects such as Slider, Locator, and Button that specifies whether they should automatically take action whenever the mouse pointer is over them, ...
AutoDelete is an option for boxes that specifies whether a box is automatically deleted when its contents are edited.