The slip rule does not extend to permit amendment of an order to include a substantive proviso that was not sought at the time of the original order because the solicitor was uninstructed on the matter and it did not occur to him to raise it — such an omission is an afterthought, not an accidental slip. The two-stage inquiry requires the court first to determine whether the slip rule applies without reference to subsequent extraneous events, and only then to consider whether subsequent events make it inexpedient or inequitable to grant the amendment.
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