Typing Unicode

[Graham Samuel]

I'm not sure if this is OT or not. I'm about to offer users of a desktop app (Mac and Windows) the ability to input some mathematical symbols, along with ordinary alphanumeric text. Clearly these symbols will be processed by the program as Unicode characters, since soon we will have "Unicode just works" for real. But my users are going to want to type these characters easily, using a conventional keyboard, which has very few such symbols, or - what? A soft keyboard, as on a touchscreen device (I'm using one to write this message on my iPad)? Or a dropdown list? Or some kind of multikey processing routine? Or something else? And how cross-platform is it possible to get?

Has anyone else worked on this problem and if so, what was the most ergonomic solution?

TIA

Graham