On registering each participant obtains a Participant Identification Code (PIC, 9-digit number)  which acts as its unique identifier in the Participant Register. A participant needs to register only  once – the information provided can be further updated or re-used by the participant in other  European Commission's calls for tenders or calls for proposals. At any moment during the procurement procedure the Research Executive Agency Validation  Services (hereafter  the EU Validation Services) may contact the participant and ask for  supporting documents on legal existence and status [and financial capacity]. The requests will be  made through the register's messaging system to the e-mail address of the participant's contact  person indicated in the register. It is the responsibility of the participant to provide a valid e-mail  address and to check it regularly.  The documents that may be requested by  the EU Validation Services  are listed in the EU Grants  and Tenders Rules on Legal Entity Validation, LEAR appointment and Financial Capacity  assessment. Economic operators can submit a tender either as a sole tenderer or as a group of tenderers. In  either case subcontracting is permitted. In order to fulfil the selection criteria set out in  Section 3.2 the tenderer can rely on the  capacities of subcontractors or other entities (not subcontractors).  The role of each entity involved in a tender (hereafter referred to as  involved entity ) must be  clearly specified: sole tenderer, member of a group or Group leader, subcontractor or an entity on  whose capacities the tenderer relies to fulfil the selection criteria$^{20}$. This applies also where the  involved entities  belong to the same economic group.  Tenderers are invited to apply in English to facilitate the selection process.  A joint tender is a situation where a tender is submitted by a group (with or without legal form)  of economic operators regardless of the link they have between them. The group as a whole is  considered a tenderer$^{21}$. All members of the group assume joint and several liability towards the  Contracting authority for the performance of the contract as a whole. 2.4.1. Joint tenders  2.4. Ways to submit a tender    Please note that a request for supporting documents by the  EU Validation Services  in no  way implies that the tenderer has been successful.  $^{20}$ Such an entity is not considered a subcontractor, see Section 2.4.3.  $^{21}$ References to  tenderer  or  tenderers  in this document shall be understood as covering both sole tenderers and  groups of economic operators submitting a joint tender.  25