indexing
	description: "Group of EV_FIGURE's. If a figure is added tothis group, it is removed from its previous group first."
	status: "See notice at end of class"
	keywords: "group, figure"
	date: "$Date$"
	revision: "$Revision$"

class interface
	EV_FIGURE_GROUP

create 

	default_create
			-- Create without point.

	make_with_point (a_point: EV_RELATIVE_POINT)
			-- Create on a_point.
			-- (from EV_SINGLE_POINTED_FIGURE)
		require -- from EV_SINGLE_POINTED_FIGURE
			a_point_not_void: a_point /= void

feature -- Initialization

	list_make (n: INTEGER)
			-- Allocate list with n items.
			-- (n may be zero for empty list.)
			-- (from ARRAYED_LIST)
		require -- from ARRAYED_LIST
			valid_number_of_items: n >= 0
		ensure -- from ARRAYED_LIST
			correct_position: before

	make_filled (n: INTEGER)
			-- Allocate list with n items.
			-- (n may be zero for empty list.)
			-- This list will be full.
			-- (from ARRAYED_LIST)
		require -- from ARRAYED_LIST
			valid_number_of_items: n >= 0
		ensure -- from ARRAYED_LIST
			correct_position: before
			filled: full

	make_from_array (a: ARRAY [EV_FIGURE])
			-- Create list from array a.
			-- (from ARRAYED_LIST)
		require -- from ARRAY
			array_exists: a /= void
	
feature -- Access

	cursor: CURSOR
			-- Current cursor position
			-- (from ARRAYED_LIST)

	first: EV_FIGURE
			-- Item at first position
			-- (from ARRAYED_LIST)
		require -- from CHAIN
			not_empty: not is_empty

	group: EV_FIGURE_GROUP
			-- Parent of Current.
			-- (from EV_FIGURE)

	has (v: EV_FIGURE): BOOLEAN
			-- Does v appear in array?
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from ARRAY)
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not is_empty

	frozen id_object (an_id: INTEGER): IDENTIFIED
			-- Object associated with an_id (void if no such object)
			-- (from IDENTIFIED)
		ensure -- from IDENTIFIED
			consistent: Result = void or else Result.object_id = an_id

	index: INTEGER
			-- Index of item, if valid.
			-- (from ARRAYED_LIST)

	index_of (v: like item; i: INTEGER): INTEGER
			-- Index of i-th occurrence of item identical to v.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- 0 if none.
			-- (from CHAIN)
		require -- from LINEAR
			positive_occurrences: i > 0
		ensure -- from LINEAR
			non_negative_result: Result >= 0

	item: like first
			-- Current item
			-- (from ARRAYED_LIST)
		require -- from TRAVERSABLE
			not_off: not off
		require -- from ACTIVE
			readable: readable
		require else -- from ARRAYED_LIST
			index_is_valid: valid_index (index)

	i_th (i: INTEGER): EV_FIGURE
			-- Entry at index i, if in index interval
			-- Was declared in ARRAY as synonym of @.
			-- (from ARRAY)
		require -- from TABLE
			valid_key: array_valid_index (k)

	last: like first
			-- Item at last position
			-- (from ARRAYED_LIST)
		require -- from CHAIN
			not_empty: not is_empty

	frozen object_id: INTEGER
			-- Unique for current object in any given session
			-- (from IDENTIFIED)
		ensure -- from IDENTIFIED
			valid_id: id_object (Result) = Current

	sequential_occurrences (v: EV_FIGURE): INTEGER
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		ensure -- from BAG
			non_negative_occurrences: Result >= 0

	orientation: DOUBLE
			-- Angle of first point of Current.
			-- (from EV_FIGURE)

	pebble: ANY
			-- Data to be transported by pick and drop mechanism.
			-- (from EV_FIGURE)

	pebble_function: FUNCTION [ANY, TUPLE, ANY]
			-- Returns data to be transported by pick and drop mechanism.
			-- When not Void, pebble is ignored.
			-- (from EV_FIGURE)

	point: EV_RELATIVE_POINT
			-- First point of Current.
			-- (from EV_SINGLE_POINTED_FIGURE)

	point_array: ARRAY [EV_COORDINATE]
			-- points as absolute coordinates.
			-- (from EV_FIGURE)
		ensure -- from EV_FIGURE
			same_length: Result.count = points.count

	point_count: INTEGER
			-- Current has one point.
			-- (from EV_SINGLE_POINTED_FIGURE)

	pointer_style: EV_CURSOR
			-- Cursor displayed when pointer is over this figure.
			-- (from EV_FIGURE)

	target_name: STRING
			-- Optional textual name describing Current pick and drop hole.
			-- (from EV_ABSTRACT_PICK_AND_DROPABLE)

	world: EV_FIGURE_WORLD
			-- Top-level parent of Current.
			-- (from EV_FIGURE)

	infix "@" (i: INTEGER): EV_FIGURE
			-- Entry at index i, if in index interval
			-- Was declared in ARRAY as synonym of item.
			-- (from ARRAY)
		require -- from TABLE
			valid_key: array_valid_index (k)
	
feature -- Measurement

	count: INTEGER
			-- Number of items.
			-- (from ARRAYED_LIST)

	index_set: INTEGER_INTERVAL
			-- Range of acceptable indexes
			-- (from CHAIN)
		ensure -- from INDEXABLE
			not_void: Result /= void
		ensure then -- from CHAIN
			count_definition: Result.count = count

	occurrences (v: like item): INTEGER
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from CHAIN)
		ensure -- from BAG
			non_negative_occurrences: Result >= 0

	occurrences (v: like item): INTEGER
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from CHAIN)
		ensure -- from BAG
			non_negative_occurrences: Result >= 0
	
feature  -- Measurement

	capacity: INTEGER
			-- Number of available indices
			-- Was declared in ARRAY as synonym of count.
			-- (from ARRAY)
		ensure then -- from ARRAY
			consistent_with_bounds: Result = upper - lower + 1
	
feature -- Status report

	after: BOOLEAN
			-- Is there no valid cursor position to the right of cursor?
			-- (from LIST)

	before: BOOLEAN
			-- Is there no valid cursor position to the left of cursor?
			-- (from LIST)

	bounding_box: EV_RECTANGLE
			-- Smallest orthogonal rectangular area Current fits in.
		ensure -- from EV_FIGURE
			not_void: Result /= void

	changeable_comparison_criterion: BOOLEAN
			-- May object_comparison be changed?
			-- (Answer: yes by default.)
			-- (from CONTAINER)

	exhausted: BOOLEAN
			-- Has structure been completely explored?
			-- (from LINEAR)
		ensure -- from LINEAR
			exhausted_when_off: off implies Result

	Extendible: BOOLEAN is True
			-- May new items be added? (Answer: yes.)
			-- (from DYNAMIC_CHAIN)

	full: BOOLEAN
			-- Is structure filled to capacity?
			-- (from ARRAYED_LIST)

	has_capture: BOOLEAN
			-- Are all events sent to Current?
			-- (from EV_FIGURE)

	invalid_rectangle: EV_RECTANGLE
			-- Rectangle that needs erasing.
			-- Void if no change is made.

	is_empty: BOOLEAN
			-- Is structure empty?
			-- (from FINITE)

	is_inserted (v: EV_FIGURE): BOOLEAN
			-- Has v been inserted at the end by the most recent put or
			-- extend?
			-- (from ARRAYED_LIST)

	is_sensitive: BOOLEAN
			-- Is object sensitive to user input?
			-- (from EV_FIGURE)

	is_show_requested: BOOLEAN
			-- Will Current be displayed when its parent is?
			-- (from EV_FIGURE)

	isfirst: BOOLEAN
			-- Is cursor at first position?
			-- (from CHAIN)
		ensure -- from CHAIN
			valid_position: Result implies not is_empty

	islast: BOOLEAN
			-- Is cursor at last position?
			-- (from CHAIN)
		ensure -- from CHAIN
			valid_position: Result implies not is_empty

	object_comparison: BOOLEAN
			-- Must search operations use equal rather than =
			-- for comparing references? (Default: no, use =.)
			-- (from CONTAINER)

	off: BOOLEAN
			-- Is there no current item?
			-- (from CHAIN)

	prunable: BOOLEAN
			-- May items be removed? (Answer: yes.)
			-- (from ARRAYED_LIST)

	readable: BOOLEAN
			-- Is there a current item that may be read?
			-- (from SEQUENCE)

	update_rectangle: EV_RECTANGLE
			-- Rectangle that needs redrawing.
			-- Void if no change is made.

	valid_cursor (p: CURSOR): BOOLEAN
			-- Can the cursor be moved to position p?
			-- (from ARRAYED_LIST)

	valid_cursor_index (i: INTEGER): BOOLEAN
			-- Is i correctly bounded for cursor movement?
			-- (from CHAIN)
		ensure -- from CHAIN
			valid_cursor_index_definition: Result = ((i >= 0) and (i <= count + 1))

	valid_index (i: INTEGER): BOOLEAN
			-- Is i a valid index?
			-- (from ARRAYED_LIST)
		ensure then -- from INDEXABLE
			only_if_in_index_set: Result implies ((i >= index_set.lower) and (i <= index_set.upper))
		ensure then -- from CHAIN
			valid_index_definition: Result = ((i >= 1) and (i <= count))

	valid_index (i: INTEGER): BOOLEAN
			-- Is i a valid index?
			-- (from ARRAYED_LIST)
		ensure then -- from INDEXABLE
			only_if_in_index_set: Result implies ((i >= index_set.lower) and (i <= index_set.upper))
		ensure then -- from CHAIN
			valid_index_definition: Result = ((i >= 1) and (i <= count))

	writable: BOOLEAN
			-- Is there a current item that may be modified?
			-- (from SEQUENCE)
	
feature -- Status setting

	compare_objects
			-- Ensure that future search operations will use equal
			-- rather than = for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		ensure -- from CONTAINER
			object_comparison

	compare_references
			-- Ensure that future search operations will use =
			-- rather than equal for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion
		ensure -- from CONTAINER
			reference_comparison: not object_comparison

	disable_capture
			-- Disable grab of all events on world.
			-- (from EV_FIGURE)
		require -- from EV_FIGURE
			in_world: world /= void
		ensure -- from EV_FIGURE
			capture_released: not has_capture

	disable_sensitive
			-- Make object non-sensitive to user input.
			-- (from EV_FIGURE)
		ensure -- from EV_FIGURE
			insensitive_requested: not internal_is_sensitive

	enable_capture
			-- Grab all mouse events for world.
			-- (from EV_FIGURE)
		require -- from EV_FIGURE
			in_world: world /= void
		ensure -- from EV_FIGURE
			capture_set: has_capture

	enable_sensitive
			-- Make object sensitive to user input.
			-- (from EV_FIGURE)
		ensure -- from EV_FIGURE
			sensitive_requested: internal_is_sensitive

	hide
			-- Request that Current not be displayed even when its group is.
			-- (from EV_FIGURE)
		ensure -- from EV_FIGURE
			not_is_show_requested: not is_show_requested

	intersects (r: EV_RECTANGLE): BOOLEAN
			-- Does r intersect Currents bounding_box?
			-- (from EV_FIGURE)

	set_point (a_point: EV_RELATIVE_POINT)
			-- Assign a_point to point.
			-- (from EV_SINGLE_POINTED_FIGURE)
		require -- from EV_SINGLE_POINTED_FIGURE
			a_point_not_void: a_point /= void
		ensure -- from EV_SINGLE_POINTED_FIGURE
			point_assigned: point = a_point

	set_target_name (a_name: STRING)
			-- Assign a_name to target_name.
			-- (from EV_ABSTRACT_PICK_AND_DROPABLE)
		require -- from EV_ABSTRACT_PICK_AND_DROPABLE
			a_name_not_void: a_name /= void
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			target_name_assigned: a_name /= target_name and a_name.is_equal (target_name)

	show
			-- Request that Current be displayed when its group is.
			-- True by default.
			-- (from EV_FIGURE)
		ensure -- from EV_FIGURE
			is_show_requested: is_show_requested

	snap_to_grid
			-- Move all move handles to most nearby point on the grid.
		require
			world_not_void: world /= void
			grid_enabled: world.grid_enabled
	
feature -- Cursor movement

	back
			-- Move cursor one position backward.
			-- (from ARRAYED_LIST)
		require -- from BILINEAR
			not_before: not before

	finish
			-- Move cursor to last position if any.
			-- (from ARRAYED_LIST)
		ensure then -- from CHAIN
			at_last: not is_empty implies islast
		ensure then -- from ARRAYED_LIST
			before_when_empty: is_empty implies before

	forth
			-- Move cursor one position forward.
			-- (from ARRAYED_LIST)
		require -- from LINEAR
			not_after: not after
		ensure then -- from LIST
			moved_forth: index = old index + 1

	go_i_th (i: INTEGER)
			-- Move cursor to i-th position.
			-- (from ARRAYED_LIST)
		require -- from CHAIN
			valid_cursor_index: valid_cursor_index (i)
		ensure -- from CHAIN
			position_expected: index = i

	go_to (p: CURSOR)
			-- Move cursor to position p.
			-- (from ARRAYED_LIST)
		require -- from CURSOR_STRUCTURE
			cursor_position_valid: valid_cursor (p)

	move (i: INTEGER)
			-- Move cursor i positions.
			-- (from ARRAYED_LIST)
		ensure -- from CHAIN
			too_far_right: (old index + i > count) implies exhausted
			too_far_left: (old index + i < 1) implies exhausted
			expected_index: (not exhausted) implies (index = old index + i)

	search (v: like item)
			-- Move to first position (at or after current
			-- position) where item and v are equal.
			-- If structure does not include v ensure that
			-- exhausted will be true.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from BILINEAR)
		ensure -- from LINEAR
			object_found: (not exhausted and object_comparison) implies equal (v, item)
			item_found: (not exhausted and not object_comparison) implies v = item

	start
			-- Move cursor to first position if any.
			-- (from ARRAYED_LIST)
		ensure then -- from CHAIN
			at_first: not is_empty implies isfirst
		ensure then -- from ARRAYED_LIST
			after_when_empty: is_empty implies after
	
feature -- Element change

	append (s: SEQUENCE [EV_FIGURE])
			-- Append a copy of s.
			-- (from SEQUENCE)
		require -- from SEQUENCE
			argument_not_void: s /= void
		ensure -- from SEQUENCE
			new_count: count >= old count

	extend (v: like item)
			-- Add v to end.
			-- Do not move cursor.
			-- Was declared in ARRAYED_LIST as synonym of force.
			-- (from ARRAYED_LIST)
		require -- from COLLECTION
			extendible: extendible
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure then -- from BAG
			one_more_occurrence: occurrences (v) = old (occurrences (v)) + 1

	fill (other: CONTAINER [EV_FIGURE])
			-- Fill with as many items of other as possible.
			-- The representations of other and current structure
			-- need not be the same.
			-- (from COLLECTION)
		require -- from COLLECTION
			other_not_void: other /= void
			extendible

	force (v: like item)
			-- Add v to end.
			-- Do not move cursor.
			-- Was declared in ARRAYED_LIST as synonym of extend.
			-- (from ARRAYED_LIST)
		require -- from SEQUENCE
			extendible: extendible
		ensure then -- from SEQUENCE
			new_count: count = old count + 1
			item_inserted: has (v)

	put (v: like item)
			-- Replace current item by v.
			-- (Synonym for replace)
			-- (from CHAIN)
		require -- from COLLECTION
			extendible: extendible
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure then -- from CHAIN
			same_count: count = old count

	put_front (v: like item)
			-- Add v to the beginning.
			-- Do not move cursor.
			-- (from ARRAYED_LIST)
		ensure -- from DYNAMIC_CHAIN
			new_count: count = old count + 1
			item_inserted: first = v

	put_left (v: like item)
			-- Add v to the left of current position.
			-- Do not move cursor.
			-- (from ARRAYED_LIST)
		require -- from DYNAMIC_CHAIN
			extendible: extendible
			not_before: not before
		ensure -- from DYNAMIC_CHAIN
			new_count: count = old count + 1
			new_index: index = old index + 1

	put_right (v: like item)
			-- Add v to the right of current position.
			-- Do not move cursor.
			-- (from ARRAYED_LIST)
		require -- from DYNAMIC_CHAIN
			extendible: extendible
			not_after: not after
		ensure -- from DYNAMIC_CHAIN
			new_count: count = old count + 1
			same_index: index = old index

	remove_pebble
			-- Make pebble Void and pebble_function `Void,
			-- Removing transport.
			-- (from EV_FIGURE)
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			pebble_removed: pebble = void and pebble_function = void

	set_accept_cursor (a_cursor: EV_CURSOR)
			-- Set a_cursor to be displayed when the screen pointer is over a
			-- target that accepts pebble during pick and drop.
			-- (from EV_FIGURE)
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			accept_cursor_assigned: accept_cursor.is_equal (a_cursor)

	set_deny_cursor (a_cursor: EV_CURSOR)
			-- Set a_cursor to be displayed when the screen pointer is not
			-- over a valid target.
			-- (from EV_FIGURE)
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			deny_cursor_assigned: deny_cursor.is_equal (a_cursor)

	set_origin (an_origin: EV_RELATIVE_POINT)
			-- Change origin of all points to o without moving.
			-- (from EV_FIGURE)

	set_pebble (a_pebble: like pebble)
			-- Assign a_pebble to pebble.
			-- (from EV_FIGURE)
		require -- from EV_ABSTRACT_PICK_AND_DROPABLE
			a_pebble_not_void: a_pebble /= void
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			pebble_assigned: pebble = a_pebble

	set_pebble_function (a_function: FUNCTION [ANY, TUPLE, ANY])
			-- Set a_function to compute pebble.
			-- (from EV_FIGURE)
		require -- from EV_ABSTRACT_PICK_AND_DROPABLE
			a_function_not_void: a_function /= void
			a_function_takes_two_integer_open_operands: a_function.valid_operands ([1, 1])
		ensure -- from EV_ABSTRACT_PICK_AND_DROPABLE
			pebble_function_assigned: pebble_function = a_function

	set_pointer_style (a_cursor: like pointer_style)
			-- Assign a_cursor to pointer_style.
			-- (from EV_FIGURE)
		require -- from EV_FIGURE
			a_cursor_not_void: a_cursor /= void
		ensure -- from EV_FIGURE
			pointer_style_assigned: pointer_style = a_cursor
	
feature -- Removal

	prune (v: like item)
			-- Remove first occurrence of v, if any,
			-- after cursor position.
			-- Move cursor to right neighbor.
			-- (or after if no right neighbor or v does not occur)
			-- (from ARRAYED_LIST)
		require -- from COLLECTION
			prunable: prunable

	remove_left
			-- Remove item to the left of cursor position.
			-- Do not move cursor.
			-- (from ARRAYED_LIST)
		require -- from DYNAMIC_CHAIN
			left_exists: index > 1
		require else -- from DYNAMIC_LIST
			not_before: not before
		ensure -- from DYNAMIC_CHAIN
			new_count: count = old count - 1
			new_index: index = old index - 1

	remove_right
			-- Remove item to the right of cursor position
			-- Do not move cursor
			-- (from ARRAYED_LIST)
		require -- from DYNAMIC_CHAIN
			right_exists: index < count
		ensure -- from DYNAMIC_CHAIN
			new_count: count = old count - 1
			same_index: index = old index
	
feature -- Transformation

	swap (i: INTEGER)
			-- Exchange item at i-th position with item
			-- at cursor position.
			-- (from ARRAYED_LIST)
		require -- from CHAIN
			not_off: not off
			valid_index: array_valid_index (i)
		ensure -- from CHAIN
			swapped_to_item: item = old i_th (i)
			swapped_from_item: i_th (i) = old item
	
feature -- Conversion

	linear_representation: LINEAR [EV_FIGURE]
			-- Representation as a linear structure
			-- (from LINEAR)
	
feature -- Duplication

	duplicate (n: INTEGER): like Current
			-- Copy of sub-list beginning at current position
			-- and having min (n, count - index + 1) items.
			-- (from ARRAYED_LIST)
		require -- from CHAIN
			not_off_unless_after: off implies after
			valid_subchain: n >= 0
	
feature -- Action sequences

	conforming_pick_actions: EV_NOTIFY_ACTION_SEQUENCE
			-- Actions to be performed when a pebble that fits this hole is
			-- picked up from another source.
			-- (when drop_actions.accepts_pebble (pebble))
			-- (from EV_FIGURE)

	drop_actions: EV_PND_ACTION_SEQUENCE
			-- Actions to take when pick and drop transport drops on Current.
			-- (from EV_FIGURE)

	pick_actions: EV_PND_START_ACTION_SEQUENCE
			-- Actions to be performed when pebble is picked up.
			-- (from EV_FIGURE)

	pointer_button_press_actions: EV_POINTER_BUTTON_ACTION_SEQUENCE
			-- Actions to be performed when screen pointer button is pressed.
			-- (from EV_FIGURE)

	pointer_button_release_actions: EV_POINTER_BUTTON_ACTION_SEQUENCE
			-- Actions to be performed when screen pointer button is released.
			-- (from EV_FIGURE)

	pointer_double_press_actions: EV_POINTER_BUTTON_ACTION_SEQUENCE
			-- Actions to be performed when screen pointer is double clicked.
			-- (from EV_FIGURE)

	pointer_enter_actions: EV_NOTIFY_ACTION_SEQUENCE
			-- Actions to be performed when screen pointer enters widget.
			-- (from EV_FIGURE)

	pointer_leave_actions: EV_NOTIFY_ACTION_SEQUENCE
			-- Actions to be performed when screen pointer leaves widget.
			-- (from EV_FIGURE)

	pointer_motion_actions: EV_POINTER_MOTION_ACTION_SEQUENCE
			-- Actions to be performed when screen pointer moves.
			-- (from EV_FIGURE)

	proximity_in_actions: EV_PROXIMITY_ACTION_SEQUENCE
			-- Actions to be performed when pointing device comes into range.
			-- (from EV_FIGURE)

	proximity_out_actions: EV_PROXIMITY_ACTION_SEQUENCE
			-- Actions to be performed when pointing device goes out of range.
			-- (from EV_FIGURE)
	
feature -- Events

	position_on_figure (x, y: INTEGER): BOOLEAN
			-- Is (x, y) on this figure?
			-- Always returns False, but descendants can override
			-- it to improve efficiency.
	
feature -- Iteration

	do_all (action: PROCEDURE [ANY, TUPLE [EV_FIGURE]])
			-- Apply action to every item.
			-- Semantics not guaranteed if action changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			action_exists: action /= void

	do_if (action: PROCEDURE [ANY, TUPLE [EV_FIGURE]]; test: FUNCTION [ANY, TUPLE [EV_FIGURE], BOOLEAN])
			-- Apply action to every item that satisfies test.
			-- Semantics not guaranteed if action or test changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			action_exists: action /= void
			test_exits: test /= void

	for_all (test: FUNCTION [ANY, TUPLE [EV_FIGURE], BOOLEAN]): BOOLEAN
			-- Is test true for all items?
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= void

	there_exists (test: FUNCTION [ANY, TUPLE [EV_FIGURE], BOOLEAN]): BOOLEAN
			-- Is test true for at least one item?
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exits: test /= void
	
feature -- List operations

	force_i_th (fig: like item; i: INTEGER)
			-- Add fig to the group.
		ensure -- from ARRAY
			inserted: i_th (i) = v
			higher_count: count >= old count

	insert (fig: like item; i: INTEGER)
			-- Add fig to the group.
		require -- from ARRAYED_LIST
			index_small_enough: pos <= count
			index_large_enough: pos >= 1
		ensure -- from ARRAYED_LIST
			new_count: count = old count + 1
			index_unchanged: index = old index
			insertion_done: i_th (pos) = v

	merge_left (other: like Current)
			-- Merge other into group before cursor.
			-- other will be empty afterwards.
		require -- from DYNAMIC_CHAIN
			extendible: extendible
			not_before: not before
			other_exists: other /= void
		ensure -- from DYNAMIC_CHAIN
			new_count: count = old count + old other.count
			new_index: index = old index + old other.count
			other_is_empty: other.is_empty
		ensure then -- from DYNAMIC_LIST
			other_empty: other.is_empty

	merge_right (other: like Current)
			-- Merge other into group after cursor.
			-- other will be empty afterwards.
		require -- from DYNAMIC_CHAIN
			extendible: extendible
			not_after: not after
			other_exists: other /= void
		ensure -- from DYNAMIC_CHAIN
			new_count: count = old count + old other.count
			same_index: index = old index
			other_is_empty: other.is_empty
		ensure then -- from DYNAMIC_LIST
			other_empty: other.is_empty

	prune_all (fig: like item)
			-- Remove fig from the group.
		require -- from COLLECTION
			prunable
		ensure -- from COLLECTION
			no_more_occurrences: not has (v)
		ensure then -- from DYNAMIC_CHAIN
			is_exhausted: exhausted
		ensure then -- from ARRAYED_LIST
			is_after: after

	remove
			-- Remove item from figure.
		require -- from ACTIVE
			prunable: prunable
			writable: writable
		ensure then -- from DYNAMIC_LIST
			after_when_empty: is_empty implies after
		ensure then -- from ARRAYED_LIST
			index: index = old index

	replace (fig: like item)
			-- Add fig to the group.
		require -- from ACTIVE
			writable: writable
		ensure -- from ACTIVE
			item_replaced: item = v

	wipe_out
			-- Unreference all groups.
		require -- from COLLECTION
			prunable
		ensure -- from COLLECTION
			wiped_out: is_empty
		ensure then -- from DYNAMIC_LIST
			is_before: before
	
feature -- Recomputation

	calculate_absolute_position
			-- Recalculates all absolute positions inside this group.

	invalidate
			-- Some property of Current has changed.

	validate
			-- Invalidate Current.
	
invariant

		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)
		-- from EV_FIGURE
	points_not_void: points /= void
	points_correct_size: points.count = point_count
	points_items_not_void: all_points_exist (points)
		-- from ARRAYED_LIST
	prunable: prunable
	starts_from_one: lower = 1
	empty_means_storage_empty: is_empty implies all_default
		-- from ARRAY
	area_exists: area /= void
	consistent_size: capacity = upper - lower + 1
	non_negative_count: count >= 0
	index_set_has_same_count: valid_index_set
	index_set_has_same_bounds: ((index_set.lower = lower) and (index_set.upper = lower + count - 1))
		-- from RESIZABLE
	increase_by_at_least_one: minimal_increase >= 1
		-- from BOUNDED
	valid_count: count <= capacity
	full_definition: full = (count = capacity)
		-- from FINITE
	empty_definition: is_empty = (count = 0)
	non_negative_count: count >= 0
		-- from INDEXABLE
	index_set_not_void: index_set /= void
		-- from LIST
	before_definition: before = (index = 0)
	after_definition: after = (index = count + 1)
		-- from CHAIN
	non_negative_index: index >= 0
	index_small_enough: index <= count + 1
	off_definition: off = ((index = 0) or (index = count + 1))
	isfirst_definition: isfirst = ((not is_empty) and (index = 1))
	islast_definition: islast = ((not is_empty) and (index = count))
	item_corresponds_to_index: (not off) implies (item = i_th (index))
	index_set_has_same_count: index_set.count = count
		-- from ACTIVE
	writable_constraint: writable implies readable
	empty_constraint: is_empty implies (not readable) and (not writable)
		-- from BILINEAR
	not_both: not (after and before)
	before_constraint: before implies off
		-- from LINEAR
	after_constraint: after implies off
		-- from TRAVERSABLE
	empty_constraint: is_empty implies off
		-- from DYNAMIC_CHAIN
	extendible: extendible

end -- class EV_FIGURE_GROUP