foo1.cs

    public override bool Accepts(IDeclaredElement declaredElement, ISubstitution substitution)
    {
      switch (declaredElement)
      {
        case ISymbolAlias symbolAlias:
        {
          var aliasedSymbol = symbolAlias.GetAliasedSymbol();
          if (aliasedSymbol == null) return true;

          return Accepts(aliasedSymbol.Element, aliasedSymbol.Substitution);
        }

        case INamespace _:
          return true;
        default:
          return myPredicate(declaredElement);
      }
    }

foo2.cs

    public override bool Accepts(IDeclaredElement declaredElement, ISubstitution substitution)
    {
      switch (declaredElement)
      {
        case ISymbolAlias (aliasedSymbol: var (element, subst)):
          return Accepts(element, subst);
        case ISymbolAlias _:
          return true;
        case INamespace _:
          return true;
        default:
          return myPredicate(declaredElement);
      }
    }

foo3.cs

    public override bool Accepts(IDeclaredElement declaredElement, ISubstitution substitution)
    {
      return declaredElement switch
      {
        ISymbolAlias (aliasedSymbol: var (element, subst)) => Accepts(element, subst),
        ISymbolAlias _ => true,
        INamespace _ => true,
        _ => myPredicate(declaredElement)
      };
    }