Hi

If I understand, you want a 3 elements structure where is true but isn't. In these sentences, precising a binary relation symbol properties, you can try to see as an order relation (perhaps the most common binary predicates are order or equivalence relations).

In such context, says that for any , there is a (for ), and that for any , there is a .

Then I guess you can quite easily define a partial order on three elements such that any two of them have a sup, but there are two with no inf (and in fact more: with no lower bound).