Simple predicate for instantiating a GFD domain variable to an element of its domain. It starts with the smallest element, and upon backtracking tries successive elements until the entire domain has been explored, at which point the predicate fails.
If Var is already a ground integer, then this predicate simply succeeds exactly once without leaving a choicepoint.
Note that this predicate is an alias for using the indomain_min method of try_value/2.