at identifies a particular episode.

For example, given the following case fragment,

        01 Jun 03    15 Oct 03    02 Nov 03    21 Dec 03
ABC        2.5          3.2          2.9          2.7
DEF        6.3          1.9          3.4          2.6
JKL        red          orange       yellow

ABC at JKL is “yellow” is 2.9

DEF at max ABC < 2