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trait Foo[F1[F1_P]]
trait Bar[F2[F2_P]]
class Test {
def barFoo[F3[F3_P]]: Foo[F3] = ???
// Now we can define a couple of type aliases:
type M[X1] = String
type N[X2] = Bar[M]
// val ok1: Foo[N] = barFoo
// Foo[?F3] <:< Foo[Test.this.N]
// [X2]Test.this.N[X2] <:< [F3_P]?F3[F3_P]
// Test.this.N[X2] <:< ?F3[X2]
// true, ?F3=N
// val ok2: Foo[({type L[X] = Bar[M]})#L] = barFoo[N]
val nok: Foo[({type L[X3] = Bar[M]})#L] = barFoo /* Type inference can't unify F with L */
// Foo[?F3] <:< Foo[[X3]Bar[[X1]String]]
// [X3]Bar[[X1]String] <:< ?F3
// [X3]Bar[[X1]String] <:< [F3_P]?F3[F3_P]
// Bar[[X1]String] <:< ?F3[X3]
// X3 <:< [X1]String
// false
}
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