whose capacities the tenderer relies to fulfil the selection criteria$^{22}$. This applies also where the  involved entities  belong to the same economic group.  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$^{23}$. All members of the group assume joint and several liability towards the  Contracting authority for the performance of the contract as a whole. Group members must appoint a  Group leader  and a single point of contact authorised to act  on their behalf in connection with the submission of the tender and all relevant questions,  clarification requests, notifications, etc., that may be received during the evaluation, award  and until the contact signature. The model power of attorney attached in  Annex 3  is to be used . The joint tender must clearly indicate the role and tasks of each member and of the  Group leader  who will act as the  Contracting authority 's contact point for the contract's administrative or  financial aspects and operational management. The  Group leader  will have full authority to bind  the group and each of its members during contract execution. If the joint tender is successful, the  Contracting authority shall sign the contract with the Group leader, authorised by the other  members to sign the contract on their behalf via power of attorney drawn up in the model  attached in  Annex 3 .  Changes in the composition of the group during the procurement procedure (after the submission  deadline and before contract signature) shall lead to rejection of the tender except in case of a  merger or takeover of a member of the group (universal succession), provided that the new entity  has access to procurement (see  Section 2.2 ) and is not in an exclusion situation, (see  Section  3.1 ).  In either case the selection criteria must be still fulfilled by the group and the terms of the  originally submitted tender may not be altered substantially, i.e. all the tasks assigned to the  excluded/rejected entity must be taken over by the group, the change must not make the tender  non-compliant with the Tender specifications, and the evaluation of award criteria of the  originally submitted tender may not be modified.  Subcontracting is the situation where the contractor enters into legal commitments with other  economic operators which will perform part of the contract on its behalf. The contractor  retains full liability towards the  Contracting authority for performance of the contract as a  whole. 19 $^{23}$ 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.  $^{22}$ Such an entity is not considered a subcontractor, see Section 2.4.3.  Subcontracting  2.4.2 Joint tenders  2.4.1