If you set up the staff as polyphonic, you would place two notes with the same start position, pitch, and length in different voices and flip the stem on one of them, for example. (as they are different voices in actuality.)
If you set up the staff as polyphonic, you would place two notes with the same start position, pitch, and length in different voices and flip the stem on one of them, for example. (as they are different voices in actuality.)