1 | initial version |

You are looking to substitute some `x_i`

by `0`

into `f`

To get the `x_i`

, you can use (i chose `k=3`

, `n=7`

in this example):

```
sage: B.gens()
(x0, x1, x2, x3, x4, x5, x6)
```

For example, to select the first `k`

inderetminates, you can do:

```
sage: B.gens()[:k]
(x0, x1, x2)
```

For the substitution, you have to produce a dictionary whose keys are the selected indeterminates and the values are always `0`

:

```
sage: in_dict = {g:0 for g in B.gens()[:k]}
sage: in_dict
{x2: 0, x1: 0, x0: 0}
```

Then you can make your substitution:

```
sage: f
x0 + x1*x3 + x1*x6 + x2*x4 + x3*x5 + x3
sage: f.subs(in_dict)
x3*x5 + x3
```

2 | No.2 Revision |

You are looking to substitute some `x_i`

by `0`

into `f`

To get the `x_i`

, you can use (i chose `k=3`

, `n=7`

in this example):

```
sage: B.gens()
(x0, x1, x2, x3, x4, x5, x6)
```

~~For example, to ~~To select the first `k`

inderetminates, you can do:

```
sage: B.gens()[:k]
(x0, x1, x2)
```

For the substitution, you have to produce a dictionary whose keys are the selected indeterminates and the values are always `0`

:

```
sage: in_dict = {g:0 for g in B.gens()[:k]}
sage: in_dict
{x2: 0, x1: 0, x0: 0}
```

Then you can make your substitution:

```
sage: f
x0 + x1*x3 + x1*x6 + x2*x4 + x3*x5 + x3
sage: f.subs(in_dict)
x3*x5 + x3
```

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