
<ConsistencyModule:> element(?Index, +Collection, ?Value)

   Value is the Index'th element of the integer collection Collection.

Arguments
   ?Index              A (domain) variable or an integer (array notation accepted).
   +Collection         A non-empty collection of integers or (domain) variable.
   ?Value              A (domain) variable or an integer (array notation accepted).

Type
   library(gfd)

Description
This constraint can be used in a variety of programs to state a
   relation between two domain variables.  Collection is a collection of 
   integers and the constraint states that its Index'th element is equal to 
   Value, i.e.


			     Collection_Index = Value

   the domain of the other variable is updated accordingly. Index starts from 1.

   Note that unlike the element constraint in IC, the values in Collection 
   can be domain variables as well as integers. Also note that the actual
   Gecode constraint has an index that starts from 0 - a dummy element
   is added to start of Collection to map Index to ECLiPSe style index
   starting from 1. A version of this constraint that uses the native 
   Gecode indexing is element_g/3. 

   This constraint can be embedded in a constraint expression in its
   functional form (without the last argument).

   ConsistencyModule is the optional module specification to give the 
   consistency level for the propagation for this constraint: 
   gfd_bc for bounds consistency, and gfd_gac for domain (generalised arc) 
   consistency.
 
   This constraint is known as element in the global constraint catalog,
   and is implemented with Gecode's element() constraint.



Fail Conditions
   Fails if Value is not the Index'th element of Collection.

Examples
   
[eclipse 2]: element(I, [1,3,6,3], V).

I = I{[1 .. 4]}
V = V{[1, 3, 6]}


[eclipse 2]: element(I, [1,3,6,3], V),  V #\= 3.

I = I{[1, 3]}
V = V{[1, 6]}

[eclipse 2]:  X :: [1..10], gfd_gac: element(I, [1,X,6,3],  V), V #\= 3.


Z = Z{[1 .. 10]}
I = I{[1 .. 3]}
V = V{[1, 2, 4 .. 10]}




See Also
   element_g / 3, ic : element / 3, ic_symbolic : element / 3, fd : element / 3
