digraph G {
ab -> cd
ab -> CD [tailclip=false]
AB -> CD [headclip=false]
AB -> cd [tailclip=false, headclip=false]
}
digraph G {
ab -> cd
ab -> CD [tailclip=false]
AB -> CD [headclip=false]
AB -> cd [tailclip=false, headclip=false]
}