TheAirline.Models.Airlines.Airline.RemoveAlliance C# (CSharp) Method

        public void RemoveAlliance(Alliance alliance)
        {
            lock (Alliances)
            {
                if (Alliances.Contains(alliance))
                {
                    Alliances.Remove(alliance);
                }
            }
        }

 public void RemoveMember(Airline airline)
 {
     AllianceMember member = Members.FirstOrDefault(m => m.Airline == airline);
     Members.Remove(member);
     airline.RemoveAlliance(this);
 }