Table 2

The EM operators

EM operation
Definition

Overlap (x ○ y)
x and y overlap if they have a part in common.
Disjoint (x ι y)
x and y are disjoint if they share no parts in common.
Binary product (x . y)
The parts that x and y share in common.
Difference (x - y)
The largest portion of x which has no part in common with y.
Binary sum (x + y)
The set consisting of individuals x and y.

In each case x and y refer to two wholes. The first two operators are Boolean and pertain to whether two wholes share any parts in common; whereas the remainder return either the parts, or, in the case of binary sum, the wholes, that satisfy the operation.

Eilbeck et al. Genome Biology 2005 6:R44   doi:10.1186/gb-2005-6-5-r44