Discontinuities in Narratives 
Alexander Nakhimovsky 
Department of Computer Science 
Colgate University 
Hamilton, NY 13346 
saaha%colgate.csnet@ relay.cs.net 
ABSTRACT 
This paper is concenled with heuristics for seg- 
menting narratives into units that form the basic ele- 
ments of discourse representations and that constrain 
the application of focusing algorithms. The following 
classes of di~ontinuities are identified: figure-ground, 
space, time, perspective, and topic. It is suggested 
that rhetorical relations between narrative units are 
mac~o labels that stand for frequently occurring clus- 
ters of discontinuities. Heuristics for identifying 
discontinuities are presented and illustrated in an 
extended example. 
1. The Segmentation Problem. 
1.1. Introduction 
Thi~; paper is concerned with heuristics for segmenting nar- 
ratives into units that tb~t the basic elements of discourse 
representations and that constrain the application of focusing 
algorithmr,. The importance of proper segmentation is frequently 
mentioned; as one text says, "the need for segmentation is 
ahnost universally agreed upon .... A good model of 
segmentation is essential to simplify the problem of understand- 
ing discourse. In particular, it divides the problem into two 
major subproblems: what techniques are needed to analyze the 
sentence.'; within a segment and how segments can be related to 
each other" (Allen 1987: 398-399). However, "there is little 
consensus on what the segments of a particular discourse should 
be or how segmentation could be accomplished. One reason for 
this lack of consensus is that there is no precise definition of what 
a segmen! is beyond the intuition that certain sentences naturally 
group together" (ibid.). A brief discussion of our position is 
therefore in order, addressing the following questions: What is it 
that is being segmented? What is the dominant feature of a seg- 
ment? What is the purpose of the segmentation process? 
We adopt the position that reading a narrative, like taking 
part in a eo~wersation, is a form of soci',d interaction. However, 
the nature of the interaction is quite different in narratives and 
conversations, and so are the principles of segmentation and the 
nature of the resulting segments. The time of a conversation 
coincides with the time of its content. Sinmltaneity in time is 
typically accompanied by a tight integration between linguistie 
and non-linguistic behavior: the verbalization of how-to-get- 
there directions is the action of giving directions, task-oriented 
conversations between an expert and apprentice are an integral 
part of p~rforming the task at hand, and the unfolding text of aa 
William J. Rapaport 
Graduate Group in Cognitive Science 
and 
Department of Computer Science 
State University of New York at Buffalo 
Buffalo, NY 14260 
rapapon@ cs.bu ffalo.edu 
argumentative dialogue is precisely the activity of arguing. 
Conversation can thus properly be called performative discourse. 
By contrast, the content of a narrative is decoupled from the 
linear progression of its text and unfolds in its own, separate 
timeline. 
It follows that in place of the situation of discourse, a narra- 
tive is processed with respect to a constantly maintained deictic 
center, which is "the locus in conceptual space-time of the 
objects and events depicted or described by the sentences 
currently being perceived. At any point in the narrative, the cog- 
nitive agent's attention is focused on particular characters (and 
other objects) standing in particular temporal and spatial relations 
to each other. Moreover, file agent 'looks' at the narrative from 
the perspective of a particular character, spatial location and tem- 
poral location. Thus the deictic center consists of a WHERE- 
point, a WHEN-point and a WHO-point." (Bruder et at. 1986: 
1). In this paper, the WHEN-point of the deictic center is 
referred to as the Temporal Focus (cf. Webber 1987a,b; Nakhi- 
movsky 1987b). 
We conceive of discourse segments (DSs) as continuous 
stretches of text corresponding to relatively monolithic pieces of 
internal representation. What "relatively monolithic" means is 
the subject of much of the rest of the paper; at this point, we sim- 
ply say that the DS remains the same as long as the deictic center 
does not undergo drastic changes in space, time, perspective or 
composition, while the beginning of a new DS is 
accompanied/signaled by a discontinuity in one or several of 
these parameters. Within each segment, reference and anaphora 
ate processed by local algorithms mostly relying on recency lists 
as in Sidner (1983). At the beginning of a new DS, a more global 
search through the accumulated representation is required. 
We thus have three kinds of entities organized into three 
kinds of structures: linearly ordered stretches of text forming the 
Linear Text Structure (LTS); the Event-Situation Structure (ESS, 
ef. Webber 1987b), representing the narrative's unfolding con- 
tents; and the Current Focus Space, which is a collection of 
focusing mechanisms (including the deictic center) that together 
represent the "attentional state" (Grosz & Sidner 1986) of the 
system. The components of the LTS are frequently linked by 
rbetodcal relationg such as elaboration, resumption or flashback 
(see, e.g., Hobbs 1982). We believe that these rhetorical rela- 
tions are simply macro labels that stand for certain oft-repeated 
clusters of discontinuities in the ESS. It is the discontinuities that 
are essential for constructing the ESS; the rhetorical labels need 
not be recognized by the reader at all, just as, on the sentence 
465 
level, speech acts need not be recognized in order to understand 
the intention of the speaker (Cohen & Levesque 1987). 
The foregoing has sewed to motivate the need for reliable 
segmentation heuristics. Most such heuristics found in the iitera~ 
ture are syntactical in nature, relying, in almost Eliza-like 
fashion, on clue words and phrases (see references in Grosz & 
Sidner 1986: 177). We pt~pose that heuristics should be based 
on semantical considerations such as discontinuities in the 
representation. This paper investigates four kinds of discontinui- 
ties: discontinuities of topic, discontinuities of space and time, 
discontinuities of figure and ground, and discontinuities of the 
narrative perspective. Section 2 explains what these are; the 
remainder of this section gives a preliminary and paltial illustra- 
tion and reviews related work. 
1.2 An example 
Consider the following example: 
(1) (a) Hartley and Phoebe had been sent by their mother to fix 
the tail vane of the windmill. (b) In the great expanse of the 
prairie where they live(I, the high tower of the windmill was 
the only teal landmark. (Worline 1956: 1) 
Rhetorically speaking, sentence (b) interrupts a sequence of 
events described in (a) (= DS1) to start DS2, a description, fit 
order to recognize this rhetorical relation between the two DSs, it 
is necessary to recognize that: 
(1) there is a shift of topic; 
(2) there is a shift in perceptual modality to visuai percep- 
tion; 
(3) there is a shift in time scale ,from the events of the 
cun'ent day to years or decades, associated with the lifetime 
of a windmill and the 'where they lived' clause; 
(4) there is shift in Sl~tial scale from a household to the 
entire prairie; 
(5) there is a shift from a foregrounded sequence of events 
to the "mopping-up" operation of filling in the background; 
the shift is signaled by aspectual changes (Hopper 1978; 
Nakhimovsky 1987b, 1988); and 
(6) the foregrounded sequence of events includes two telic 
processes (walking fi'om rite house to the windmill; fixing 
the broken part) whose beginnings or preconditions are 
explicitly mentioned but whose terminal points are still in 
the future relative to the Temporal Focus; this sets up 
expectations for the reader. 
The following empirical investigation is suggested by this 
and similar' examples: classify the discontinuities and clusters of 
discontinuities that typically accompany DS breaks in narratives; 
identify rite linguistic and extra-linguistic knowledge involved; 
develop heuristics for using this knowledge; and test the heuris- 
tics in a computer program. Section 2 below discusses nma-ative 
representations mid the data structures that ale needed for con.- 
structing and updating them. A classification of discontinuities 
falls out of this discussion. Section 3 presents several kinds of 
knowledge that we consider relevant for identifying discontinui- 
466 
ties in narratives. Section 4 illustrates the colresponding heuris- 
tics with an extended example Whose point is that our heuristics 
explain the use of deietic devices attd con'ecfly predict paragraph 
breaks observed in existing narratives.'i 
1.3. Related work 
Centt~al to our investigation is the idea that text underst~md- 
ing involves "building a good structure" (Bruce 1981: 283) by 
the process of snccessive embedding of the cut~ent sentence 
representation into the stEa~cture created by the preceding text. 
This idea emerged almost simultmleously in Computational 
Linguistics/Al (Bruce 1981; Weber 1979, 1983) and linguistics 
(Kamp 1981, Heim 1982). (There has al~ been interaction, 
more o1' less conscious, with the Re,",der--Response school of 
literary criticism as represented in, e.g., Thompkins 1981.) The 
main difference between these two developments concerns the 
role of inference and monotonicity: to what extent doe, s the 
structure being built incorporate defea.sible inferences that may 
have to be undone? We do not pursue this issue hele but assume 
non~-monotonic embeddability and an active role fbr expectations 
set up by the text. (Cf. N~himovsky 1988 for some discussion.) 
Grosz & Sidner (1986) is the first unified approach in which 
the problem of segmentation is fled up with the notion of atten.. 
tional state. As argued in Nakhimovsky (1987b), some features 
of their model (a stack mechanism for attentional state, the prom~ 
inenee of pragmatic notions such as the speaker's intentions) 
make it more appropriate for conversation rather than na~cative~ 
Webber (1988) and Naidlimovsky (1988) suggest a model in 
which the distinction between the top and the rest of die stack is 
replaced by the distinction between a sh~nt~tel'm memory and the 
ESS. 
Ottr work has been developing in close contact with the 
SUNY Buffalo Graduate Group in Cognitive Science's p~'ojcct on 
cognitive and computer systems for understanding narrative text. 
This research program consists of a group of projects whose 
goals are to develop a psychologically real model of' a cognitive 
agent's comprehension of deictic infbnnation in nan'ative text. 
The hypothesis of this project is that the eonstrtiction and 
modification of the deictic center is important fox ~ comprehension. 
To test tiffs hypothesis, a computer system implemented in 
SNePS (Shapiro 1979, Shapiro & Rapaport 1987) is being 
developed that wilt "read" a narrative and answer questions con- 
renting the reader's beliefs about the objects, relations, and 
events in ito "l~e system will be psychologically real, because the 
details of the algorithms and the efficacy of the linguistic devices 
will be validated by psychological experiments on nolmal ar, d 
abnormal comprehenders. ((~. Bruder et al. 1986, Daniels 1986, 
Ahneida 1987, Wiebe & Rapapolt 1988.) 
Thence is surprisingly little psychological work on discourse 
seganentation. To rem.edy this situation, a series of expelJments 
I" This is not to suggest timt tyl~ogmphical pacag~aph breaks are the 
only discontinuities we ate afar. First, ~t tile minimal level of seg- 
mentation, DSs are ust'tally smaller than typographical paragraphs. 
Second, a typographical paragraph does not simply sigJlat or suggest 
a discontinuity: it creates one by its reD' pJ'esenc.~;. 
is being de,,;igned and condncted at Colgate (Reynolds & Nakhi- 
movsky (in preparation)). The gubjects are being asked to 
segment narratives of varions gemes and stpactural characteris- 
tics and later recall them, under conditions of both cued and 
uncued ~eeatl. We proceed from the hypothesis that narrative 
structures as they arc remembered are different from such strnc- 
tures as they are built "on line" in the process of comprehension. 
2o Narrative~ and Their lltepr~ntatlon~. 
For the purposes of this paper, we adopt the simplest narra~ 
five model. There is only one, objective, narrator, who gives an 
observer account of the story. The story consists of descriptions 
of situation,; evolving or persisting in time. Loosely following 
Hayes (1995), we call these descriptions history-~okens, or h~ 
token,s tbr slto~. (l,exieal meanings are history-types (h-types) 
related to iheh" h-tokens by the relation of "non-monotonic 
emtnMdability".) The time of a narrated h-token is determined 
with respecl to a specific point within the previously muratexl h- 
tokens~ and usually without reference to the time of discourse.\] ~ 
Using Reiehenbach's notion of refel~ence time, we can say that a 
sentence in a narrative never has the time of discourse as its 
reference tiaie. Put differently, a sentence in a present tense 
necessarily ~ntennpts a nan'ative, unless it is int~preted as histor- 
ical (narrative) present. 
Tl~e meaning of a non-generic sentence in a narrative is a 
collection of h-tokens together with the position of the deictic 
center (to lhe extent that it is uniquely specified by the sentence). 
After the first sentence of a nm'rative establishes the initial set-up, 
each subsequent sentence is processed ill the context consisting 
of the ESS and ttte Current Focus Space. Depending on the 
meaning of the sentence, one of two things happens: either the 
representation of the sentence is incorporated in the Current 
Focus Space, with the focusing mechanisms appropriately 
modified, or, in the case of a focus shift, the contents of the 
Current Foeus Space are incorporated into the Event-Situation 
Slxucture (ESS) ~md Linear Text Stmctore (LTS), and the Current 
Focus Space is completely reset. The nature of the processing at 
the DS juncOtre is thus quite different fiom the "routine" tasks 
m be performed as long as the text remains in the same DS: the 
start of a lle't,v DS prompts, and is prompted by, a shift of atten- 
tion. The (ircularity here is deliberate. The start of a new DS 
brings al~t~t several c~,anges, some of them more immediately 
noticeable thorn others; file mole obvious ones serve to signal that 
a new DS is, indeed, started. We p~oceed to catalog the changes. 
Th~ lost obsetvali~n to make is that a nan'ative must have a 
plot, i.e., p~e~ent ~ sequ~mce of events that forms an inslamce of a 
recognizable pattern. (The patto-n.,; are part universal, part 
culture-.specific; the work of Lehnert (1982) and Alker et al. 
i In spoken narratives about eve~L,; that (axe presented its having) ac.. 
ta~lly oecun'ed, rite namator nmy occ~L~ionally make ~eference to the 
time of discom'se (by b,-.ginnh~g a new discotlrse segment with, e.g., 
"Then, yesterday, 1 ran into 8mid~ mid he told me..."); however, 
oven in |his case, hltegration with ttie previously narrated events is 
obligatory. 
(1985) can be seen as a search for the principles on which such 
patterns are built.) Using Gestalt terminology (brought into 
linguistics by Tahny (1983)), we can say that a narrative's plot 
must present a recognizable temporal/eansal figure shown against 
some ground that minimally consists of spatial/visual settings 
(descriptions of characters are also frequent). The distinction is 
not always clear-cut, because elements of the figure can be hid- 
den among the details of the ground, but the temporal nature of 
the plot does stand in clear contrast to the spatial nature of the 
ground. 
Secondly, a narrative must have characters with whom we 
empathize. These characters don't have to be human: one Can 
easily imagine a story about an adventuresome plant seed that 
falls off its parent, gets swallowed and excreted by a horse, and 
nearly drowns in a tropical rain before being miraculously saved 
by the sun and producing a flower. Even so, the narrative is 
likely to alternate between die objective narrator's point of view 
and that of one of the characters. ("The belly of the horse was 
dark and noisy inside.") 
Suppose for a moment that the ESS is implemented as a par- 
titioned network of nodes, each node representing a narrated h- 
token and partitions corresponding to the belief spaces of the 
characters. An unfolding narrative then creates a path through 
the network such that it, and the inferences it generates, covers 
the network in its entirety. Some discontinuities of narratives 
very simply reflect the inlrinsic spatial or temporal discontinui- 
ties of the plot, e.g., when the story is composed of a sequence of 
events taking place during an afternoon, followed by two years' 
hiatus, followed by another action-packed afternoon. (A similar 
example of a spatial discontinuity can be easily imagined.) One 
measure of the "simplicity" of a narrative is how faithfully the 
order and stntcturing of its text reflects the order and structuring 
of its component events. Even in the simplest narrative, how~ 
ever, there are bound to be discontinuities resulting from the ten- 
sion between the linear nature of the text and the multi- 
dimensional structure that it is meant to evoke. These are discon- 
tinuities of figure and ground, when the narrative shifts between 
the main story-line and the surrounding circumstance, and 
discontinuities of perspective, when the narrative crosses into a 
different "empathy partition" or creates a new one. 
Given this classification of discontinuities, one can proceed 
to catalog the clues that signal them. This is a subject for a large 
empirical study, of which the next section is but a preliminary 
sketch. It is important to keep in mind that it is clusters of 
discontinuities that signal the beginning of a new DS. 
3. Discontinuities in Narratives. 
3.1. Topic discon\[inuities. 
Discontinuities of topic faLl into two groups. In the first, 
there is no anaphoric relation or immediate inference path from 
the new topic to a node in the Current Focus Space. What an 
"immediate inference path" is depends, of course, on the 
system's knowledge base and inferential capabilities, but this is a 
467 
separate issue that is not dealt with in this paper. Of more 
interest to us is the second kind of discontinuity, when an 
anaphoric relation exists and calls for a pronominal anaphor, but 
the WHO-point is instead reintroduced by a full noun phrase, e.g. 
(unless otherwise indicated, the examples below are from Joyce 
1969 \[1914\]): 
(2) \[The barmbracks\] had been cut into long thick slices and 
were ready to be handed round at tea. Mafia had cut them 
herself. 
Maria was a very, very small person indeed... 
3.2. Temporal discontinuities. 
The most important temporal discontinuities are: 
a. A shift from perfective to imperfective sentence perspective 
accompanied by a shift to a much greater time scale. The 
corresponding rhetorical move is frequently characterized as 
"introducing background or descriptive material". The 
move is frequently accompanied by a topic re-introduction. 
b. The reverse shift from descriptive material to the main line 
of the narrative. This move is signaled by the TF and the 
entire deictie center, returning to an established node in the 
ESS, with an appropriate contraction of the time scale. 
c. A backwards move of the TF to an earler point in time, with 
or without a change in time scale. Rhetorically, this is 
known as flashback. This move is frequently signaled by a 
verb in past perfect or by the used to + Infinitive construc- 
tion, although a shift may occur without such a verb form, 
and the presence of such a verb form does not necessarily 
signal a shift: the reference time of the sentence may remain 
the same as, rather than precede, the current TF. (See 
Almeida (1987) and Nakhimovsky (1988) for a more 
detailed discussion.) 
3.3. Spatial discontinuities. 
The most obvious spatial discontinuities are discontinuities 
of scale. It is argued at some length in Nakhimovsky (1986, 
1987a) that h-types have time scales associated with them, 
characterized in terms of "received" cyclical events such as day 
or year. It seems equally necessary to establish a gradation of 
spatial scales, based on similar considerations from human biol- 
ogy and habitat. The spatial scales we currently employ are: 
one's body (which may need to be further specialized); within 
arm's reach; room area, such as desk or bed; room; floor; house; 
household; village/neighborhood; larger area within a between- 
meals round trip; within a day's round trip; staying overnight. 
(The larger the scale, the more domain- and culture-specific vail- 
ation there is.) 
A change in spatial scale is frequently accompanied by 
related phenomena such as a change in temperature or lighting: 
(3) She changed her blouse too and, as she stood before the mir- 
ror, she thought of how she used to dress for mass on Sun- 
day morning when she was a young girl; and she looked 
with quaint affection at the diminutive body which she had 
so often adorned. In spite of its years she found it a nice 
tidy little body. 
468 
When she got outside the streets were shining with rain and 
she was glad of her old brown raincloak. 
3.4. Perspective discontinuities. 
The following signals frequently indicate a shift to a 
character's subjective perspective away from the objective per- 
spective of the implied narrator: (a) attitude reports, which can 
be further subeategorized into beliefs, desires, emotions, and so 
on; communication verbs; and perceptions; and (b) deictics. 
Attitude reports, by their very nature, introduce private semantic 
objects into the ESS and thus create, or move into, a partition. 
Deictics, such as the verbs bring or come, indicate the position of 
the WHO-point of the deictie center; a shift of this position to 
one of the characters signals a discontinuity. (Cf. Banfield 1982, 
Wiebe & Rapaport 1988.) 
4. An Example. 
This section of the paper applies the above heuristics to the 
initial fragment of Joyce's "Clay' '. The fragment falls into three 
DSs: sentence 1 (DS1), sentences 2-6 (DS2), and sentences 6-12 
(DS3).t Embedded in DS3 is DS3.1, consisting of sentences 9.. 
10. Sentence 13 starts a fourth DS by returning to the first one. 
1. The matron had given her leave to go out as soon as the 
women's tea was over and Mafia looked forward to her evening 
out. 2. The kitchen was spick and span: the cook said you could 
see yourself in the big copper boilers. 3. The fire was nice and 
bright and on one of the side-tables were four very big bann- 
bracks. 4. These barmbracks seemed uncut; but if you went 
closer you would see that they had been cut into long thick even 
slices and were ready to be handed round at tea. 5. Mafia had 
cut them herself. 
6. Maria was a very, very small person indeed but she had a very 
long nose and a very long chin, 7. She talked a little through her 
nose, always soothingly: Yes, my dear, and No, my dear. 8. She 
was always sent for when the women quarrelled over their tubs 
and always succeeded in making peace. 9. One day the matron 
had said to her:--Maria, you are a veritable peace-maker! 10. 
And the sub-matron and two of the Board ladies had heard the 
compliment. 11. And Ginger Mooney was always saying what 
she wouldn't do to the dummy who had charge of the irons if it 
wasn't for Maria. 12. Everyone was so fond of Maria. 
13. The women would have their tea at six o'clock and she would 
be able to get away before seven. 
The transition from sentence 1 to 2 is very similar to the 
transition from (a) to (b) in example (1): it is a shift from figure 
to ground marked primarily by tense and aspect changes and a 
shift from temporal to spatial/visual material. The change in 
time and space scales is not as dramatic here, but there is the 
t'II~esc intuitive divisions, two of which correspond to Joyce's para- 
graph breaks, have been Confirmed by one of the experiments report- 
ed in Reynolds and Nakhirnovsky (in preparation). 
sane arrangement of nanated events that are prior to the Tem- 
poral Focus ("The matron had given her leave...") and antici- 
pated events that are in the future with respect to the Temporal 
Focus (the women's tea, Maria's evening out). This sets up 
expectations suspended by the visual matedM and stative verbs. 
Sentence 5, by using an action verb and the past-perfect tense, 
return to the time scale and the temporal a~rangernent of sentence 
1. 
The transition from 5 to 6 (paragraph break) is characterized 
by a shift ia time scale and a topic re-introduction. The material 
is a (back)ground character description: 'Maria is such that...' 
The hegira,Aug of" DS3.1 is signaled by a well-known clue phrase 
One day and by the past-perfect tense. Note that the material is 
still gronnd ('Mmia is such that...'). "the precise relationship 
between I)S3 and DS3.1 is at this p~fint ambiguous: they cmt be 
siblings, a ltd they wouM be if sentences 11 and 12 were dropped 
fi'om the nmxafive. Howevcr~ sentence 11 clearly signals a returu 
to the material of sentences 6-8: the tense changes back from 
past perfect to past (past progressive, presumably for a sharper 
contrast with the perfect), and the adverb always, used in sen° 
tences 7 and 8, reappears again. 'Ibis establishes that DS3.1 is, 
indeed, embedded in DS3; note that it bears no relation to DS1, 
and, in pmticular, the pastq~erfect events of sentences 9-10 are 
much fm'ther in the past (on a different time scale) than the past 
perfect events of sentence 1. 
The tJ ansition from 12 to 13 (the next paragraph break) is a 
retina to the event sequence of senteuce 1. The position of the 
TF, amt the entire deictic center is indicated by the future-in-the~ 
past tense. Note that it is essential to retrieve the entire deictic 
center, and not just the 'I'I,', because the WHO-point is also 
restored: the she in 13 does not evoke Maria of sentence 12 or 
any other sentence in DS 2 and 3 presented from the perspective 
of the implied narrator. Rather, this pronoun is a quasi-indexical 
(Rapaport 1986) that replaces the first-person singular I of 
Maria's fit, mghts and expectations, signaled by Maria looked for- 
ward in sentence 1.t 
5. Future research. 
There: are several directions in which we are proceeding. 
Wiebe & Rapaport (1988) and Wiebe (in progress) present an 
outline of a detailed computational investigation of narrative per- 
specfive and reference. Reynolds & Nakhimovsky (in prepara- 
tion) will report on several psychological experiments designed 
to obtain empirical data on how people segment narratives in the 
process of reacting, and how they are segmented when recalled. 
The deicti¢ center project (Bruder et at. (1986)) contains both a 
linguistic t;tudy of the role of indexicals in narrative segmentation 
1In contrast to the naive children's story of Example 1, it is difficult 
to make definite starements about the narrative perspective in Joyce. 
Even his early stories, anticipating the incoming medenfism, deli.- 
berately and skillfully blend the character's perspective with the im- 
plied ruartator's, so that even a descriptiou of Maria uses colloquial 
vocabulary and syntax that suggest a hum,'m voice that could l~e ouly 
Mafia's. 
and a computational project that will test all the diverse segmen- 
tation he~wisties within the unifoma system of belief representa-. 
tion. 
Acknowledgments. 
This research was supported in part by NSF Grant No. IR1- 
8610517. We are grateful to Mary Galbraith and Janyce M. 
Wiebe for comments on an earlier version, and to Bonnie 
Webber and Rebecca Passonneau for discussions of related work. 

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