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A lambda function is a kind of anonymous map. For example:

sage: f = lambda x : 2*x

Says "f is the map that sends x to 2*x", and you can check:

sage: f(4)
8

It is anonymous because you can do:

sage: (lambda x : 3*x)(3)
9

Then, you can get the documentation of xmrange_iter by typing:

sage: xmrange_iter?

This makes your residues the image of a product by a map.

Indeed, the first part of res is the list of lists (to be understood as a product):

sage: res.iter_list
[[-1, 0, 1, 2], [-1, 0, 1, 2]]

and its second part is the map that has to be mapped to any element of the product:

sage: res.typ
<function sage.rings.number_field.number_field_ideal.<lambda>>

This second argument is the lambda function you want to understand. Let us play with it:

sage: res.typ((-1,-1))
-a - 1
sage: res.typ((-1,0))
-1
sage: res.typ((0,1))
a
sage: res.typ((0,2))
2*a
sage: res.typ((3,2))
2*a + 3

I am sure you understand what does this lambda function!

Now, the list of residues is just the image of each element of the product $\{-1, 0, 1, 2\} \times \{-1, 0, 1, 2\}$ by the map $(u,v) \mapsto au + v1$, that is:

sage: list(res)
[-a - 1,
 -1,
 a - 1,
 2*a - 1,
 -a,
 0,
 a,
 2*a,
 -a + 1,
 1,
 a + 1,
 2*a + 1,
 -a + 2,
 2,
 a + 2,
 2*a + 2]

sage: res.cardinality()
16

A lambda function is a kind of anonymous map. For example:

sage: f = lambda x : 2*x

Says "f is the map that sends x to 2*x", and you can check:

sage: f(4)
8

It is anonymous because you can do:

sage: (lambda x : 3*x)(3)
9

Then, you can get the documentation of xmrange_iter by typing:

sage: xmrange_iter?

This makes your residues the image of a product by a map.

Indeed, the first part of res is the list of lists (to be understood as a product):

sage: res.iter_list
[[-1, 0, 1, 2], [-1, 0, 1, 2]]

and its second part is the map that has to be mapped to any element of the product:

sage: res.typ
<function sage.rings.number_field.number_field_ideal.<lambda>>

This second argument is the lambda function you want to understand. Let us play with it:

sage: res.typ((-1,-1))
-a - 1
sage: res.typ((-1,0))
-1
sage: res.typ((0,1))
a
sage: res.typ((0,2))
2*a
sage: res.typ((3,2))
2*a + 3

I am sure you understand what does this lambda function!

Now, the list of residues is just the image of each element of the product $\{-1, $ \{-1, 0, 1, 2\} \times \{-1, 0, 1, 2\}$ 2\} $ by the map $(u,v) \mapsto au + v1$, (u,v) --> a*u + v*1 , that is:

sage: list(res)
[-a - 1,
 -1,
 a - 1,
 2*a - 1,
 -a,
 0,
 a,
 2*a,
 -a + 1,
 1,
 a + 1,
 2*a + 1,
 -a + 2,
 2,
 a + 2,
 2*a + 2]

sage: res.cardinality()
16

A lambda function is a kind of anonymous map. For example:

sage: f = lambda x : 2*x

Says "f is the map that sends x to 2*x", and you can check:

sage: f(4)
8

It is anonymous because you can do:

sage: (lambda x : 3*x)(3)
9

Then, you can get the documentation of xmrange_iter by typing:

sage: xmrange_iter?

This makes your residues the image of a product by a map.

Indeed, the first part of res is the list of lists (to be understood as a product):

sage: res.iter_list
[[-1, 0, 1, 2], [-1, 0, 1, 2]]

and its second part is the map that has to be mapped applied to any element of the product:

sage: res.typ
<function sage.rings.number_field.number_field_ideal.<lambda>>

This second argument is the lambda function you want to understand. Let us play with it:

sage: res.typ((-1,-1))
-a - 1
sage: res.typ((-1,0))
-1
sage: res.typ((0,1))
a
sage: res.typ((0,2))
2*a
sage: res.typ((3,2))
2*a + 3

I am sure you understand what does this lambda function!

Now, the list of residues is just the image of each element of the product $ \{-1, 0, 1, 2\} \times \{-1, 0, 1, 2\} $ by the map (u,v) --> a*u + v*1 , that is:

sage: list(res)
[-a - 1,
 -1,
 a - 1,
 2*a - 1,
 -a,
 0,
 a,
 2*a,
 -a + 1,
 1,
 a + 1,
 2*a + 1,
 -a + 2,
 2,
 a + 2,
 2*a + 2]

sage: res.cardinality()
16

A lambda function is a kind of anonymous map. For example:

sage: f = lambda x : 2*x

Says "f is the map that sends x to 2*x", and you can check:

sage: f(4)
8

It is anonymous because you can do:

sage: (lambda x : 3*x)(3)
9

Then, you can get the documentation of xmrange_iter by typing:

sage: xmrange_iter?

This makes your residues the image of a product by a map.

Indeed, the first part of res is the list of lists (to be understood as a product):

sage: res.iter_list
[[-1, 0, 1, 2], [-1, 0, 1, 2]]

and its second part is the map that has to be applied to any element of the product:

sage: res.typ
<function sage.rings.number_field.number_field_ideal.<lambda>>

This second argument is the lambda function you want to understand. Let us play with it:

sage: res.typ((-1,-1))
-a - 1
sage: res.typ((-1,0))
-1
sage: res.typ((0,1))
a
sage: res.typ((0,2))
2*a
sage: res.typ((3,2))
2*a + 3

I am sure you understand what does this lambda function!

Now, the list of residues is just the image of each element of the product $ \{-1, 0, 1, 2\} \times \{-1, 0, 1, 2\} $ by the map (u,v) --> a*u + v*1u*1 + v*a , that is:

sage: list(res)
[-a - 1,
 -1,
 a - 1,
 2*a - 1,
 -a,
 0,
 a,
 2*a,
 -a + 1,
 1,
 a + 1,
 2*a + 1,
 -a + 2,
 2,
 a + 2,
 2*a + 2]

sage: res.cardinality()
16