The seminal decision is Willick v. Willick, 1994 CanLII 28 (SCC),  3 SCR 670 where Mr. Justice Sopinka stated at 688: ...In deciding whether the conditions for variation exist, it is common ground that the change must be a material change of circumstances. This means a change, such that, if known at the time, would likely have resulted in different terms. The corollary to this is that if the matter which is relied on as constituting a change was known at the relevant time it cannot be relied on as the basis for variation.
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