<> (what is ?x) (is ?x a (programming language))
<> (is ?x a ?y) (or, is ?x (a virtual machine))
<> (or, is ?x ?y) (?x is ?y <> ?y (a meta-language))
<> ((a meta-language)) modal
<> (?x is ?x) (?(?: ?:) ?x)
what is modal