# Poset _ ZZ -- returns an element of the ground set

## Synopsis

• Operator: _
• Usage:
a = P_i
• Inputs:
• P, an instance of the type Poset,
• i, an integer, index in the ground set
• Outputs:
• a, , the $i$-th vertex in the ground set

## Description

This method allows easy access to the vertices of the poset.

 i1 : P = booleanLattice 3; i2 : P_0 o2 = 000 i3 : P_3 o3 = 011

## See also

• Poset _ List -- returns elements of the ground set
• Poset _* -- returns the ground set of a poset
• Poset -- a class for partially ordered sets (posets)