9. The expert of IWG SLR also sought guidance on the principle “prohibited if not allowed” for the lamp installation according to UN Regulation No. 48 (GRE-91-02) and proposed three different options to incorporate this principle (GRE-91-22). Several experts from Contracting Parties expressed general preference for options A or C, but no final wording was agreed. GRE decided to revert to this issue at the next session. In the interim, experts were invited to send their comments to IWG SLR.