... Qualifiers¹

This research was supported in part by the National Science Foundation CAREER Award No. CCR-0093337, NSF CCR-9457812, NASA Contract No. NAG2-1210, NSF CCR-0085949, a UC Regents Fellowship, and an equipment donation from Intel.

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... type.²

Java uses the rule (Wrong) for arrays. In Java, if S is a subclass of T, then S[] is a subclass of T[], where X[] is an array of X's. Java gets away with this by inserting run-time checks at every assignment into an array to make sure the type system is not violated. Since we seek a purely static system, Java's approach is not available to us.

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