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# element(?Index, +Values, ?Element)

Element is the Index'th element of the collection Values.
*?Index*
- A variable or an integer.
*+Values*
- A non-empty collection of numbers or variables.
*?Element*
- A variable or a number.

## Description

Values is a collection (see eval_to_array/2) of numbers or numeric
variables, and the constraint states that its Index'th element is
equal to Element.
The most common use for this constraint is to state a relation
between two variables, where one is a linear index and the other
an arbitrary value defined by an entry in a table of constants.

More generally, the table can itself contain problem variables.

If Values contains only instantiated integers, then the implementation
maintains domain-consistency between Index and Element.

If Values contains reals or domain variables, the implementation
maintains bounds-consistency for Element and the variables in Values,
and domain-consistency for Index.

### Fail Conditions

Fails if Element is not the Index'th element of Values.
### Resatisfiable

No.
## Examples

?- element(I, [1,3,6,3], V).
I = I{1 .. 4}
V = V{[1, 3, 6]}
There is 1 delayed goal.
yes.
?- element(I, [](1,3,6,3), V), V #\= 3.
I = I{[1, 3]}
V = V{[1, 6]}
There is 1 delayed goal.
yes.
?- A#::2..4, B#::8..9, C#::4..5, element(I, [A,B,C], X), X#=<7.
A = A{2 .. 4}
B = B{[8, 9]}
C = C{[4, 5]}
I = I{[1, 3]}
X = X{2 .. 5}
There is 1 delayed goal.
Yes (0.00s cpu)

## See Also

:: / 2, eval_to_array / 2