# principalFilter -- computes the elements above a given element in a poset

## Synopsis

• Usage:
F = principalFilter(P, a)
• Inputs:
• P, an instance of the type Poset,
• a, , an element of the poset
• Outputs:
• F, a list, containing all elements greater than or equal to the given element

## Description

The filter of a given element of a poset is all the elements in the poset which are greater than or equal to the element.

 i1 : P = booleanLattice 3; i2 : principalFilter(P, "101") o2 = {101, 111} o2 : List