(** For historical reasons, ZAxiomsMiniSig isn't just NZ + ZAxiom, we also add an [opp] function, that can be seen as a shortcut for [sub 0]. *)
Module Type Opp (Import T:Typ).
Parameter Inline opp : t -> t.
End Opp.
Module Type OppNotation (T:Typ)(Import O : Opp T).
Notation "- x" := (opp x) (at level 35, right associativity).
End OppNotation.
Module Type Opp' (T:Typ) := Opp T <+ OppNotation T.
Module Type IsOpp (Import Z : NZAxiomsSig')(Import O : Opp' Z).
#[global]
Declare Instance opp_wd : Proper (eq==>eq) opp.

Axiom opp_0 : - 0 == 0.