How does one generate custom symbols? For example, the physicist notation for the rotation is "nabla cross function". In this case however, Mathematica complains that the [esc]del[esc] symbol evaluates to the unary operator Del[], which of course cannot take a cross ([esc]*[esc]) after it, since a bracket is expected.
Although a correctly looking output is generated by
Prefix[f[a], "\[Del]\[Times]"]

the result cannot simply be assigned to an operation (Prefix[...] := ...) you can type in using the nicely readable [esc] commands I mentioned above. Is there some way of doing this, i.e. invoking completely custom functionality to (combinations of) existing symbols?
\[Laplace] \[Divergence] \[Curl]may be useful. – Silvia Jan 18 '12 at 23:27\[Cross](ESC cross ESC) rather than\[Times], since it's conceptually a cross product, not scalar multiplication. – Mechanical snail Nov 15 '12 at 21:29