# ApCoCoA-1:BB.ASneighbors

From ApCoCoAWiki

## borderbasis.ASneighbors

list of across-the-street neighbors

### Syntax

$borderbasis.ASneighbors(OO:LIST):LIST

### Description

Computes the list of across-the-street neighbors in the border of the order ideal OO. The input is a list OO of terms that specify an order ideal. The output is a list of quadruples <formula>[i,j,k,l]</formula> such that <formula>x_k * b_i = x_l * b_j</formula>.

#### Example

$borderbasis.ASneighbors([1,x]); [[1, 2, 2, 3], [3, 4, 2, 3], [3, 5, 1, 3], [4, 5, 1, 2]] -------------------------------