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General classes for dealing with social choice theory.

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package io.github.oliviercailloux.j_voting.preferences;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;

import io.github.oliviercailloux.j_voting.Alternative;

/**
 * An immutable preference which represents a complete pre-order, also called a
 * weak order. for each couple of alternatives (a,b) we can find an order a ≥ b
 * or b ≥ a.
 */
public interface ImmutableCompletePreference extends ImmutablePreference {

	/**
	 * The rank of an alternative is one plus the number of alternatives strictly
	 * preferred to it.
	 *
	 * @param a is an Alternative
	 * @return the rank of this alternative (a number between 1 and n) where
	 *         n is the total number of Alternative instances.
	 *
	 * @throws IllegalArgumentException if a is not contained in this preference
	 */
	public int getRank(Alternative a);

	/**
	 *
	 * @param rank at least 1.
	 * @return the Aternative set at this rank. Empty set id there is
	 *         no alternative at this rank.
	 * @throws IllegalArgumentException if rank is less than one.
	 */
	public ImmutableSet getAlternatives(int rank);

	/**
	 *
	 * @return Same data but in an Immutable list object A set of alternative is
	 *         strictly prefered to next sets.
	 *
	 *         All the alternatives in a set are considered ex-aequo.
	 */
	public ImmutableList> asEquivalenceClasses();
}