body of competent jurisdiction to be invalid or unenforceable the invalidity or unenforceability of such provision shall not affect the other provisions of this Agreement and all provisions not affected by such invalidity or unenforceability shall remain in full force and effect 25 ***Confidential treatment requested pursuant to a request for confidential treatment filed with the Securities and Exchange Commission. Omitted portions have been filed separately with the Commission. The parties hereby agree to attempt to substitute for any invalid or unenforceable provision a valid or enforceable provision that achieves to the greatest extent possible the economic, legal and commercial objectives of the invalid or unenforceable provision 26. Assignment and sub-contractors 26.1 Neither party shall be entitled to assign the benefit of this Agreement without the prior written consent of the other party nor shall such consent be unreasonably withheld. 26.2 SEV, with the consent of DCL and without incurring unnecessary expense, may sub-contract the performance of its obligations under this Agreement or any part thereof and such consent will not be unreasonably withheld. 26.3 SEV shall not engage agents or sub-contractors to provide the Maintenance Services (or any material part of the Maintenance Services) without DCL's prior consent and DCL's consent shall not be unreasonably withheld or delayed. 26.4 SEV shall remain responsible for obligations that are performed by agents or sub-contractors (and for the acts or omissions of agents and sub-contractors) as if they were acts or omissions of SEV. 27. Value Added Tax Save insofar as otherwise expressly provided, all amounts stated in this Agreement are expressed exclusive of value added tax and any value added tax arising in respect of any supply made hereunder shall on the issue of a valid tax invoice in respect of the same be paid to the party making such supply