Example:
\documentclass{article} % Something very clever here implementing \lBrace as ⦃ and \rBrace as ⦄. \begin{document} \(\lBrace s\mapsto t\widehat{\ \,\ }u \rBrace\) % Some maths here including ↦ and the wide hat ̂ . \end{document}
should produce ⦃ s ↦ t ̂u ⦄ (with the wide hat instead of the narrow one). By default, I load a bunch of other packages, including newtx, mathtools, amssymb and stmaryrd, but the open braces seem not to be there. Of course, one can tikz them in different sizes and then apply \mathpalette or even metafont them, but that would be the last resort.
Crosspost: http://tex.stackexchange.com/questions/ ... r-pdflatex