Unsharing replaces multiple occurrences of the same variable by fresh yet equal (enforced through propagators for equality) variables: after unsharing a variable appears at most once. Note that this is only done for not yet assigned variables (as all propagators can handle multiple occurrences of the same variable provided it is already assigned).

Unsharing is useful for constraints that only accept variable arrays without multiple occurrences of the same variable, for example extensional.