@model MusicianSettings
@{
     ViewBag.YetAvailableInstruments = _context.Instrument.Where(i=> !_context.MusicianSettings.Any(s=>s.UserId==id && s.Instrumentation.Any(j=>j.Id == i.Id)))
      .Select(k=>new SelectListItem { Text = k.Name });

}
<ul>
@foreach (var instrument in Model.Instrumentation)
{
    <li>@instrument.Name 
<a asp-action="RemoveInstrument" asp-controller="Instrumentation" asp-action-id="Model.UserId" asp-action-name="@instrument.Name" />

        </li>


}
</ul>

        <form asp-action="AddInstrument" asp-controller="Instrumentation" asp-action-id="Model.UserId"  >
        
            <select name="Name" value="" placeholder="Séléctionnez votre instrument" asp-items=@ViewBag.YetAvailableInstruments>
            </select>
        </form>