@article{Xiao:2024ut,
  author = "Xiao, Zhiguang  and  Zhou, Zhi-Yong",
  title = "{Theoretical aspects of virtual states, bound states, and resonances in hadron physics from Friedrichs model}",
  doi = "10.22323/1.413.0004",
  journal = "PoS",
  year = 2024,
  volume = "CD2021",
  pages = "004"
}