15. The trust instrument shall provide that, as soon as practicable after any shares have been appropriated to a participant, the trustees will give him or her notice in writing of the appropriation -
(a) specifying the number and description of those shares, and
(b) stating their initial market value.
(1) The trust instrument shall contain a provision prohibiting the trustees from disposing of any shares, except as mentioned in paragraphs (a), (b) or (c) of section 511(6), during the period of retention (whether by transfer to the participant or otherwise).
(2) The trust instrument shall contain a provision prohibiting the trustees from disposing of any shares after the end of the period of retention and before the release date except -
(a) pursuant to a direction given by or on behalf of the participant or any person in whom the beneficial interest in the participant's shares is for the time being vested, and
(b) by a transaction which would not involve a breach of t
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