Use 'Yours sincerely,' when writing to a named person. Use 'Yours faithfully,' when using the 'Dear Sir/Madam' greeting. Use the semi-formal 'Best regards,' or 'Kind regards,' if you wish the tone to be slightly less formal.
Irrevocable — Any changes (amendment) or cancellation of the LC (except it is expired) is done by the applicant through the issuing bank. It must be authenticated and approved by the beneficiary.