THE LITERARY STRUCTURE OF THE BOOK OF EXODUS 1–18: six pericopes and their chiastic lexical relation: the bar graph.
refer to verbs in past tenses,
refers to verbs in future tenses.
The table and the bar graph show that:
external pericopes I and VI have the same percentage of words in the past tenses (62%) and in the future tenses (38%)
pericopes II and V have the same percentage of words in the past tenses (56%) and in the future tenses (44%);
Central pericopes III and IV are characterized by an even more interesting relationship (in a very good mathematical approximation):
the percentage of words in the past tenses in the pericope III = the percentage of words in the future tenses in the pericope IV (35% almost equals34% )
the percentage of words in the future tenses in the pericope III = the percentage of words in the past tenses in the pericope IV (65% almost equals66%)
Thanks to these numerical dependencies, the arrangement of six pericopes is a concentric structure ABC C’B’A’; in this case biblical scholars say exactly that it is the chiasmus – a special type of the concentric structure. Such a structure is typical for Hebrews.
At the actual stage of this presentation, we know a lot about the literary structure of the Book of Exodus 1–18. In the next stage, it will be shown the identity of this literary structure with the structure of an ancient Hittite treaties of the 16th century before Christ.
 See R. Yudkowsky, Chaos or Chiasm? The Structure of Abraham’s Life, “Jewish Bible Quarterly” 35/2 (2007), 109: the author distinguishes between the structure of type A B C A’ B’ C’ (parallelism) and the structure of type A B C C’ B’ A’ (chiasmus). On page 11 he shows chiasmus composed of sixteen elements! See also: J. Synowiec, Gatunki literackie w Starym Testamencie, Kraków 2003, 37; M. Kantor, Struktury dośrodkowe i odśrodkowe w poezji biblijnej (Ps 120–134), Kraków 1988, 80–83.