+ It is also possible to use this file with abstract arrays. In this case,
+ xvec and yvec are not represented in memory. They only exist conceptually.
+ In this case, the list of defines above is amended as follows:
+ ELEMENT Undefined.
+ EQUAL Undefined.
+ XVECREF_YVECREF_EQUAL(ctxt, xoff, yoff)
+ A three-argument macro: References xvec[xoff] and
+ yvec[yoff] and tests these elements for equality.