489d7b6d72
This PR introduces antitonicity lemmas that support the elaboration of
mixed inductive-coinductive predicates defined using the
`least_fixpoint` / `greatest_fixpoint` constructs.
For instance, the following definition elaborates correctly because all
occurrences of the inductively defined predicate `tock `within the
coinductive definition of `tick` appear in negative positions. The dual
situation applies to the definition of `tock`:
```
mutual
def tick : Prop :=
tock → tick
greatest_fixpoint
def tock : Prop :=
tick → tock
least_fixpoint
end
```
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| .. | ||
| Order | ||
| Order.lean | ||