We might also consider the negations of \in, \subseteq, \subset and even perhaps < and > Larry > On 5 Mar 2016, at 22:19, Makarius <makarius at sketis.net> wrote: > > * New abbreviations for negated existence (but not bounded existence): > > ∄x. P x ≡ ¬ (∃x. P x) > ∄!x. P x ≡ ¬ (∃!x. P x)