Vasant Nanavati wrote...
....
. . . And you still say there's nothing original in these NGs?
....

Nope. The ABS(x-m)<w/2 idiom has been mentioned before for testing
whether x falls between m-w/2 and m+w/2 without having to calculate m
twice, and the ratio term is akin to the standard way of counting
distinct entries in a range containing duplicates.

The gist is that each of C, D or E must account for some but not all of
the total count of all C:E in I:K.