message: simplify InvariantT variance erasure
diff: @@ -4,19 +4,15 @@ import * as P from "../../Prelude"
  import type * as HKT from "../../Prelude/HKT"
  import type { Par } from "../../Prelude/HKT/variance"
  -type Strip<C, P extends Par, A extends HKT.Variance, B extends HKT.Variance> = Erase<
  - Erase<C, P.V<P, A>>,
  - P.V<P, B>
  ->
  -
  export function monad<P extends Par>(_: P) {
  return <F extends HKT.URIS, C>(
  M: P.Monad<F, C>
  - ): P.Monad<F, Strip<C, P, "+", "-"> & P.V<P, "_">> => P.instance(M)
  + ): P.Monad<F, Erase<C, P.V<P, "+"> & P.V<P, "-">> & P.V<P, "_">> => P.instance(M)
  }
  export function applicative<P extends Par>(_: P) {
  return <F extends HKT.URIS, C>(
  M: P.Applicative<F, C>
  - ): P.Applicative<F, Strip<C, P, "+", "-"> & P.V<P, "_">> => P.instance(M)
  + ): P.Applicative<F, Erase<C, P.V<P, "+"> & P.V<P, "-">> & P.V<P, "_">> =>
  + P.instance(M)
  }
  