> ++2.12.18!

$ copy-file changes/B.scala B.scala

$ copy-file changes/A1.scala A.scala
> run 1
$ copy-file changes/A2.scala A.scala
> run 2

> clean
> ++2.13.12!

$ copy-file changes/A1.scala A.scala
> run 1
$ copy-file changes/A2.scala A.scala
> run 2
