Each region relation corresponds to a relational operator in TC. Each
relational operator takes two forms, one *unary* and the other
*binary*. The unary form, ` op S`, generates the set
of regions that bear the relation

The binary form of a relational operator, ` R op S`,
generates all regions matching

For the sake of simplicity, all relational operators have equal
precedence and right associativity, so that `X in Y in Z` is
parsed as `X in (Y in Z)`.

Robert C. Miller and Brad A. Myers

Mon Apr 26 11:34:19 EDT 1999