The following accent commands automatically give good positioning of double accents:
\Hat \Check \Tilde \Acute \Grave \Dot \Ddot \Breve \Bar \VecWith the usual non-capitalized math accent commands, the second accent will sometimes be askew; for example:
(hat|A|). With the amsmath package, if
you type Hat|A| (using the capitalized form for both
accents) the second accent will be better positioned: 
.
This double accent operation is complicated and tends to slow down the processing of a document. If your document contains many double accents, you may wish to use the amsxtra package, which provides an accentedsymbol command. accentedsymbol is a sort of hybrid of newcommand and savebox; you use it in the preamble of your document to store the result of the double accent command in a `box' for quick retrieval.
\accentedsymbol{\Ahathat}{\Hat{\Hat A}}
The commands dddot and ddddot are available to produce triple and quadruple dot accents in addition to the dot and ddot accents already available in /.