How does the defence of autrefois acquit work?

In Van Rassel v. The Queen (1990), 1990 CanLII 124 (SCC), 53 C.C.C. (3d) 353 McLachlin J. (as she then was), writing for the court, said, at p. 360: To make the defence of autrefois acquit, the accused must show that the two charges laid against him are the same. In particular, he must prove that the following two conditions have been met: (1) the matter is the same, in whole or in part, and (2) the new count must be the same as at the first trial, or be implicitly included in that of the first trial, either in law or on account of the evidence presented if it had been legally possible at that time to make the necessary amendments.