# ApCoCoA-1:BB.ASneighbors

From ApCoCoAWiki

This article is about a function from ApCoCoA-1. |

## BB.ASneighbors

Computes a list of across-the-street neighbors.

### Syntax

BB.ASneighbors(OO:LIST):LIST

### Description

This command 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 `[i,j,k,l]` such that `x_k * b_i = x_l * b_j` where the border terms `b_i` and `b_j` correspond to the `i`-th and `j`-th element of the list returned by the command BB.Border(OO).

@param

*OO*A list of terms representing an order ideal.@return A list of across-the-street neighbors of

`OO`.

#### Example

Use QQ[x,y,z]; BB.Border([1,x]); BB.ASneighbors([1,x]); [z, y, xz, xy, x^2] ------------------------------- [[1, 2, 2, 3], [3, 4, 2, 3], [3, 5, 1, 3], [4, 5, 1, 2]] -- E.g. the first quadruple of the result can be interpreted -- as that y*z = z*y