Thanks so much for that suggestion, it's a little over my head and probably out of scope for the kind of conceptual modelling I'm doing, but I'm fascinated by all this stuff and I'm definitely going to add that to my list of conceptual jewellery stores to rob.


Awesome, cheers for that, it's very neat. I'm sure I'll incorporate that in somewhere too.

Oh that is a good call! That page mentions C.I. Lewis coined a 'possibly', '◇', which seems pretty good to me. It's used as a prefix rather than an infix but it's close enough that, unless something much better presents itself, I am going to use that. Thanks so much, both fishfry and Valentinus, for your time and thoughtful responses.

I would like to find a relatively unambiguous character in Unicode which some field has used to represent (optional or possible) (inclusion association). A possible example of use:

Sandwich ∈ Bread
Sandwich ? Cheese

where ? is the symbol I'm trying to find.