 So as to have concrete formulas to discuss, consider the instances of these three schemata with distinct sentence letters p and q taken as φ and ψ, respectively, and we will now use (1)–(3) to refer to these concrete instances. The first pair are unrestrictedly equivalent and all three are diagonally equivalent, with (3) having (1) and (2) as general consequences though not  conversely.[51]  All are diagonally equivalent to the Boolean disjunction p ∨ q, which we may put by saying that all are two-dimensional isotopes of the one-dimensional, i.e. A-free, formula p ∨ q, or, more usefully, that their respective equivalence classes w.r.t. the relation of unrestricted equivalence, stand in this ‘isotope’ relation. Similarly, we can speak of the (in the above presentation, derived) connective or as a two-dimensional isotope of the Boolean ∨, thinking of the formula (2) as a context of the variables p, q. (On the other hand, what is referred to in note 51  as Groenendijk–Stokhof’s “or” is not a two-dimensional isotope of Boolean disjunction, p or q, so understood, being diagonally equivalent to a Boolean tautology, rather than to p ∨ q.)