=Paper= {{Paper |id=Vol-2744/paper18 |storemode=property |title=Evaluation of Vector Transformations for Russian Word2Vec and FastText Embeddings |pdfUrl=https://ceur-ws.org/Vol-2744/paper18.pdf |volume=Vol-2744 |authors=Olga Korogodina,Olesya Karpik,Eduard Klyshinsky }} ==Evaluation of Vector Transformations for Russian Word2Vec and FastText Embeddings== https://ceur-ws.org/Vol-2744/paper18.pdf
            Evaluation of Vector Transformations
      for Russian Word2Vec and FastText Embeddings*

           Olga Korogodina1 [0000-0003-3601-4677], Olesya Karpik2 [0000-0002-0477-1502]
                      and Eduard Klyshinsky1 [0000-0002-4020-488X]
    1 National Research University Higher School of Economics, Moscow Myasnitskaya. 20,

                                         101000, Russia
                                   eklyshinsky@hse.ru
                 2 Keldysh Institute of Applied Mathematics, Miusskaya sq., 4

                                    Moscow, 125047, Russia
                                      parlak@mail.ru



        Abstract. Authors of Word2Vec claimed that their technology could solve the
        word analogy problem using the vector transformation in the introduced vector
        space. However, the practice demonstrates that it is not always true. In this paper,
        we investigate several Word2Vec and FastText model trained for the Russian
        language and find out reasons of such inconsistency. We found out that different
        types of words are demonstrating different behavior in the semantic space.
        FastText vectors are tending to find phonological analogies, while Word2Vec
        vectors are better in finding relations in geographical proper names. However,
        we found out that just four out of fifteen selected domains are demonstrating ac-
        curacy more that 0.8. We also draw a conclusion that in a common case, the task
        of word analogies could not be solved using a random word pair taken from two
        investigated categories. Our experiments have demonstrated that in some cases
        the length of the vectors could differ more than twice. Calculation of an average
        vector leads to a better solution here since it closer to more vectors.

        Keywords: Word Embeddings, Vector Space, Vector Transformation, Word
        Analogies.


1       Introduction

The basic point for the semantic space of natural language words was the paper [1]
published in 2003. It introduced fixed-size vectors (embeddings) generated by a neural
network using statistical information about the word context. This concept was devel-
oped in [2] where the author demonstrated that such pre-trained vectors can be useful
for solution of different problems of natural language processing. The Word2Vec mode


Copyright © 2020 for this paper by its authors. Use permitted under Creative Commons License
Attribution 4.0 International (CC BY 4.0).

*   Publication financially supported by RFBR grant №18-08-01484
2 O. Korogodina, O.Karpik, E. Klyshinsky


based on the distributive hypothesis was introduced in 2013 [3-5]. The Word2Vec
model also uses neural networks reinforced by several new ideas. First of all, the new
approach [4] had less computational complexity compared to the previous systems. The
next article [5] increases its learning rate and accuracy. And the greatest contribution
of the authors was the publication of source codes and pre-trained language models for
free use. However, the authors of these papers processed texts written only in English.
The transfer of these models into inflectional languages meets some problems because
of the large variety of tokens of the same lemma. The statistical distribution of word
forms of the given lemma is not always uniform. As a result, the model needs bigger
corpora to collect good statistics for rare forms. That is why researchers use lemmati-
zation for inflectional languages. However, some of the problems need information for
individual word forms, what brings us back to the problem of under-tuned models.
   In order to keep the important lexical information, the FastText model was intro-
duced in 2017 [6]. The authors of this model keep the following idea. Both prefixes and
postfixes of words carry semantic information as well as word roots. In this case, the
meaning of a word can be composed from the meaning of its parts. Dividing a word
into n-grams, the system collects more information about the same n-gram using con-
texts of different words. The authors of [3-5] claimed that the new semantic space al-
lows the vector arithmetic. Their example “Queen = King–man + woman” swiftly be-
comes very famous. However, it becomes clear in a short time that such operations do
not always lead us to success. One of the proofs of this concept is the problem of words
analogies. The early experiments demonstrated that another favorite example, countries
and their capitals, does not work correctly for any case – country, capital and pre-trained
language model. The accuracy of this analogy was pretty high but not enough to state
that vector arithmetic works properly. The Word2Vec and FastText models correctly
find the list of semantic neighbors for a given word, what makes it a crucial part of
modern systems of natural language processing. However, the problem of words anal-
ogies does not work as well as it could be.
   In this paper, we investigate the reasons of such deviations in accuracy. In the Sec-
tion 2, we state the problem of word analogies as a vector transformation problem. The
Section 3 gives a short review of existing vector transformation methods for the prob-
lem of word analogies. Sections 4 and 5 describe the used data set and the numerical
evaluation of free language models for the Russian language. The Section 6 analyses
the reasons of low accuracy for some categories of word analogies. The Section 7 con-
cludes the article. In this paper, we do not consider systems of the BERT and ELMO
families [7, 8]. The correct investigation of such systems needs a slight correction of
our method and will be conducted in the nearest future. The description of contextual-
ized words embedding could be found in paper [9].


2      Formal Statement of the Problem of Word Analogies

In common words, the main question of the problem of word analogies could be stated
as “Is there a word c which relates to the word b as the word a' relates to the word a?”
Answering this question, Word2Vec uses vector representation of the word. Let va' and
     Evaluation of Vector Transformations for Russian Word2Vec and FastText Embeddings 3


va be vectors corresponding to the words a' and a respectively; in this case, the vector
difference va' - va expresses the semantic relation (or in other words, the semantic dif-
ference) between the words a and a'. Thus, in order to find an analogue, we should find
the word x and its corresponding vector y such that y - vb = va' - va, or

                                  𝑦 = 𝑣𝑏 + 𝑣𝑎′ − 𝑣𝑎 .                                  (1)

    However, the probability of existence of a word having exactly the same vector as
vx is extremely small. That is why Word2Vec finds vector y' that is the closest word to
the vector y:
                      𝑦′ = 𝑎𝑟𝑔𝑚𝑎𝑥 𝑐𝑜𝑠⁡(𝑣, 𝑣𝑏 + 𝑣𝑎′ − 𝑣𝑎 )                              (2)
                            𝑣∉{𝑣𝑎,𝑣𝑎′ ,𝑣𝑏}

   We can reformulate the question for word groups. Let us consider a set of word pairs
(w11:w12), (w21:w22), …, (wN1:wN2) that have the same semantic or lexical relation, and
their corresponding vectors v11, v11, v21, v21, …, vN1, vN1. In this case, the task of word
analogies could be formulated as following: if there is a vector x that makes an affine
transformation of w11, w21, …, wN1 to w12, w22, …, wN2, then x is such that
                          𝑣𝑖2 = 𝑎𝑟𝑔𝑚𝑎𝑥 𝑐𝑜𝑠⁡(𝑣′, 𝑣𝑖1 + 𝑥 ),                             (3)
                                      𝑣′

   Let us denote the fact that the word a relates to the word b in the same sense as the
word c relates to the word d by the following equation: (a:b) :: (c:d). For example, (ap-
ple:fruit) :: (cucumber:vegetable), (apple:apples) :: (cucumber:cucumbers), and, clas-
sical, (king:queen) :: (man:woman). In this case, a request to find an analogy looks like
(king:?) :: (man:woman) or (man:woman) :: (king:?).


3      Review of Affine Transformation Methods for the Problem of
       Word Analogies

As it was mentioned above, the Word2Vec system uses an algorithm that finds the vec-
tor nearest to the calculated one [3]:
                      𝑦′ = 𝑎𝑟𝑔𝑚𝑎𝑥 𝑐𝑜𝑠⁡(𝑣, 𝑣𝑏 + 𝑣𝑎′ − 𝑣𝑎 ).                             (4)
                            𝑣∉{𝑣𝑎,𝑣𝑎′ ,𝑣𝑏}

   Such model is called 3CosAdd. As it was demonstrated in [10-15], the 3CosAdd
method has crucial drawbacks. The accuracy of this method varies depending on the
word set or the trained model [10, 11, 15]. This method is not applicable for such tasks
as analogies of synonyms and antonyms [11, 12]. Such variety could be explained by
the drawbacks of trained models and text corpora; however, the paper [13] states that
the reason is the relative ordering of vectors in the model space. Moreover, the 3Co-
sAdd method returns just one vector while in such tasks as “whole-part” there could be
a set of response vectors [14].
   That is the why researchers have to find other methods to solve the problem of word
analogies. One of them is the Only-b [16] method that takes a nearest neighbor of vb:
4 O. Korogodina, O.Karpik, E. Klyshinsky


                              𝑦′ = 𝑎𝑟𝑔𝑚𝑎𝑥 𝑐𝑜𝑠⁡(𝑣, 𝑣𝑏 ).                                      (5)
                                      𝑣∉{𝑣𝑎,𝑣𝑎′ ,𝑣𝑏}

   We suppose here that if va and vb in (1) are very close, then va - vb = 0 and y = vb.
   The next method is Ignore-a [16] that takes the vector closest to the sum of va' and
vb, i.e., finds the vector located between va' and vb:
                          𝑦′ = 𝑎𝑟𝑔𝑚𝑎𝑥 𝑐𝑜𝑠⁡(𝑣, 𝑣𝑎′ + 𝑣𝑏 )                                     (6)
                                   𝑣∉{𝑣𝑎,𝑣𝑎′ ,𝑣𝑏}

  The PairDirection [10] mehod supposes that va' - va and vb' - vb are collinear:
                      𝑦′ = 𝑎𝑟𝑔𝑚𝑎𝑥 𝑐𝑜𝑠⁡(𝑣 − 𝑣𝑏 , 𝑣𝑎′ − 𝑣𝑎 ).
                             𝑣∉{𝑣𝑎,𝑣𝑎′ ,𝑣𝑏}

  The authors of 3CosMul method show in the paper [10] that formula (2) is equal to

            𝑦′ = 𝑎𝑟𝑔𝑚𝑎𝑥 (𝑐𝑜𝑠(𝑣, 𝑣𝑎′ ) − 𝑐𝑜𝑠(𝑣, 𝑣𝑎 ) + 𝑐𝑜𝑠(𝑣, 𝑣𝑏 )).                          (7)
                  𝑣∉{𝑣𝑎,𝑣𝑎′ ,𝑣𝑏}

   The authors use an example (London:England)::(Baghdad:?). The component cos(v,
vEngland) responses to the similarity of the answer with the country, the component cos(v,
vBaghdad) responses to the cultural and geographical similarity, and the component cos(v,
vLondon) responses to the cultural and geographical difference. The correct answer is
Iraq, but the component cos(v, vBaghdad) dominates all other components and the result-
ing answer becomes Mosul. In order to eliminate such domination, the authors intro-
duce a new formula that keeps balance among the various components:
                                                    𝑐𝑜𝑠(𝑣,𝑣𝑎′ )𝑐𝑜𝑠(𝑣,𝑣𝑏 )
                          𝑦′ = 𝑎𝑟𝑔𝑚𝑎𝑥                                        ,               (8)
                                   𝑣∉{𝑣𝑎,𝑣𝑎′ ,𝑣𝑏}       𝑐𝑜𝑠(𝑣,𝑣𝑎 )+𝜀


where ε = 0.001 is a small constant eliminating division by zero.
   The task of word analogies is very sensitive to the noise in the input data. A word
can be homonymous; this means that it should be presented as two or more separate
vectors representing different meanings of this word. In case of Word2Vec, such a word
will be represented only by a vector that will be a superposition of all its meanings.
Moreover, the resulting vectors of similar entities could express differences in their
occurrence with other words. For example, a dog and a cow are both animals, but dog
is a carnivore and a human’s friend, while a cow is an herbivore and gives milk; thus,
the analogy is not complete here. In order to eliminate such influence, the authors of
the 3CosAvg method [17] introduce a new formula that takes into account not just a
pair of words but whole two groups having the same analogy:
                                                         ∑𝑛
                                                          𝑖=1 𝑣𝑎′           ∑𝑛
                                                                             𝑖=1 𝑣𝑎
                                                                    𝑖                𝑖
                  𝑦′ = 𝑎𝑟𝑔𝑚𝑎𝑥 𝑐𝑜𝑠 (𝑣, 𝑣𝑏 +                              −                )   (9)
                          𝑣∈𝑉∖{𝑣𝑏}                           𝑛                   𝑛


   As it was shown in [10, 16], methods Only-b, Ignore-a, and PairDirection give un-
satisfactory results. In the next part of our article we will compare the results of two
methods (3CosAdd and 3CosAvg) shown on different models trained in Russian.
     Evaluation of Vector Transformations for Russian Word2Vec and FastText Embeddings 5


4      Used Data Sets

We used several pre-trained models from the site RusVectōrēs
(http://rusvectores.org/ru/models/): Araneum Upos Skipgram 2018, Ruwikiruscorpora
Upos Skipgram 2018, Ruwikiruscorpora Upos Skipgram 2019, Tayga Upos Skipgram
2019, News Upos Skipgram 2019, Ruscorpora Upos CBOW 2019, Araneum Fasttext
Skipgram 2018, Facebook FastText CBOW 2018 [29, 30]. The first models were
trained using Word2Vec, the two later ones were trained using FastText.
   For semantic analogies, we used the Russian versions of Google analogy test set [4]
and BATS (The Bigger Analogy Test Set) [15]. For grammatical analogies we used
morphological dictionary of the Russian language. The list of used categories is pre-
sented in Table 1.

                   Table 1. Used semantic and grammatical categories

Category                  ID       Example                                      Number
                                                                                of Pairs
  Famous capital →
                          A1             Афины                   Греция             23
        Country
All capitals → Country    A2           Канберра               Австралия             115
 Country → currency       A3            Ангола                  кванза              30
 Country → Adjective      A4           Австралия            австралийский           41
 Country → Language       A5           Аргентина              испанский             36
Masculine → Feminine      A6           наследник              наследница            67
  Singular → Plural       A7            улыбка                  улыбки              100
  Antonyms with не-
                          A8         определенный          неопределенный           27
       (non-, ir-)
 Adjective → Adverb       A9           спокойный               спокойно             30
Possessive Adjective →
                          A10             яркий                   ярче              24
Comparative Adjective
Verb → Corresponding
  Noun with -ация (-      A11       консультировать          консультация           55
         ation)
Verb → Corresponding
  Noun with -ение (-      A12          назначать              назначение            55
      ment, -ion)
Verb → Corresponding
Noun with -тель (-er, -   A13           слушать                слушатель            56
           or)
Verb → Reflexive Verb     A14           откопаю                откопаюсь            400
Verb → Verb with при-     A15            вязать                привязать            376
6 O. Korogodina, O.Karpik, E. Klyshinsky


5      Evaluation

For the purpose of evaluation, we calculated the accuracy metrics for all category ex-
amples for the given language model. Fig.1 demonstrates the results for the 3CosAdd
method; Fig.2 demonstrates the results for the 3CosAvg method. Dark blue shows re-
sults with higher accuracy, up to 1; light blue shows results closer to zero.




                          Fig. 1. Accuracy by 3CosAdd method




                          Fig. 2. Accuracy by 3CosAvg method

   The best results for the 3CosAdd method were 0.9 for the category Country → Ad-
jective taught at the Russian Wikipedia. Note that this category demonstrates the best
results for any used language model. It is not surprising that Country categories achieve
better results on Wikipedia text model since there is more information on this topic.
   The worst results are demonstrated at reflective verbs (A14) and verbs with prefixes
(A15). In our experiments, we included not only the initial forms of the verb but a
variety of forms: the past tense, the imperative mood, etc. That is why the resulting
affine transfer vector expresses variety of characteristics, but not the only one, and
failed to find one preferential direction.
     Evaluation of Vector Transformations for Russian Word2Vec and FastText Embeddings 7


   Some words were rare in the learning corpus, and the model failed to represent a
solid vector representation for these words. That is true, for example, for the category
A10 Possessive Adjective → Comparative Adjective.
   The FastText model works better for categories with flexies: A8, A9, A11, A12,
A13. Originally, the FastText model was created to work with character n-grams and
learn grammatical features of the language. So, FastText is better situated to learn the
‘sense’ of prefixes and affixes.
   The results for 3CosAvg are much better. The category A1 Famous capital → Coun-
try demonstrates 100% accuracy on Wikipedia data. However, the results for some cat-
egories are not so impressive. The categories A14 and A15 still demonstrate the same
results by the same reasons. The category A3 Country → currency cannot be solved
better than 37%. We can suppose that the reason is that different countries have the
same name for their currency, but their vectors are different; thus, their transition vec-
tors should be different as well. Finally, the category A7 Singular → Plural faces to the
variety of Russian homonymous postfixes denoting several tags.


6      Data Analysis

In order to find out the reasons of success and fail, we conducted a visual analysis of
the Word2Vec and FastText vectors. First of all, we projected 300-dimensional vectors
into 2D-space using Principal Component Analysis (PCA). Instead of t-SNE and
UMAP, PCA does not create areas with non-linear skewing. As a result, parallel vectors
keep their parallelism. On the other hand, there is a non-zero probability that two vec-
tors on parallel planes could become parallel on the projection. The later case makes
some distortion in the data, but not as critical as the former one.
    For our experiments, we used two pre-trained language models: Araneum Upos
Skipgram 2018 and Araneum Fasttext Skipgram 2018. They were trained on the same
Araneum corpus. We randomly selected five word pairs for several categories presented
in Fig. 3-8. All vectors are directed from a blue to a red point.
    Fig. 3-8 helps us make the following conclusion. The main reason of low accuracy
in the task of word analogies is the bias between vectors. It is easy to see that Word2Vec
vectors in Fig. 3 are mostly parallel, excluding slightly bias for Рим-Италия (Rome-
Italy). The length of the vectors is also almost the same. Averaging among the begin-
ning and ending points of vectors helps adjusting these small biases in the Word2Vec
model. However, the FastText model is oriented mostly on word parts; that is why its
vectors are almost randomly oriented and have no preferential direction. The same is
true for Fig. 4. However, in Fig. 6 the situation is opposite. The difference between the
starting and finishing points here is the prefix не- (non-, ir-). The FastText model, which
vectors are parallel and have quite the same length, processes such situation better than
Word2Vec. Quite the same is true for the category A13 Verb → Noun with -тель (-er,
-or) (Fig. 8) where the FastText model achieves much better results.
8 O. Korogodina, O.Karpik, E. Klyshinsky




   Fig. 3. Word2Vec and FastText vectors for the category A1 Famous capital → Country




     Fig. 4. Word2Vec and FastText vectors for the category A14 Country → Adjective




    Fig. 5. Word2Vec and FastText vectors for the category A15 Verb → Verb with при-
    Evaluation of Vector Transformations for Russian Word2Vec and FastText Embeddings 9




  Fig. 6. Word2Vec and FastText vectors for the category A8 Antonyms with не- (non-, ir-)




      Fig. 7. Word2Vec and FastText vectors for category A14 Verb → Reflexive Verb




Fig. 8. Word2Vec and FastText vectors for the category A13 Verb → Noun
with -тель (-er, -or)
10 O. Korogodina, O.Karpik, E. Klyshinsky


   The worst situation is shown in Fig. 5 and Fig. 7 for prefix при- and reflexive verbs,
which differ from the main form by the suffix -ся or -сь. These parts of word are very
homonymous. So, prefix при- could mean approaching, connection, proximity, partial-
ity of an action, finalization of an action, etc. According to these meanings, the corre-
sponding vectors could be perpendicular or antiparallel. This results in very low accu-
racy for all used models. We used just initial forms for Fig. 5 and Fig. 7 to eliminate
the influence of grammatical features.


7      Discussion and Conclusion

In this article, we found several reasons why the vector transformation does not work
on some categories of word analogies.

1. A used language model should be taught on texts that have enough occurrences of
   words for which the task of word analogies is solved. As we can see in Fig. 1 and 2,
   categories including countries, their capitals, and other related words are better ana-
   lyzed using corpora like Wikipedia, since such corpora have enough information for
   inference of logical relations among these words. Moreover, these words are allo-
   cated in the same context in the Wikipedia text; thus, their vectors become more
   similar. Other model, which was trained on fiction or news texts, does not have the
   same context. That is why categories A1-A5 demonstrate the best results on the Wik-
   ipedia corpus. Note that this conclusion needs to be proved in an independent inves-
   tigation.
2. In a common case, the task of word analogies could not be solved using a random
   word pair taken from two investigated categories. At least, some words are homon-
   ymous, and their vectors are out of the common systems for words of the selected
   category. If these words are chosen as the basis in such methods as Word2Vec, then
   such basis will be shifted and word analogies will be found incorrectly. For example,
   Moscow and Berlin are respectful representatives of their countries in case of inter-
   national or cultural affairs; these cities are used as synonyms of Russian and German
   government and culture. However, Bogota and Kampala are rather a capital city than
   a government. Moreover, Russian prefixes and suffixes could have different mean-
   ings. Thus, there will be several preferential directions for different prefix or suffix
   values. If someone misuses just one word in a pair, he or she will get a wrong tran-
   sition vector.
  Averaging of the starting and finishing points helps to eliminate this problem. This
   helps more in the case of factual information (about 30% increment for accuracy),
   but less for grammatical information (less than 10% for Masculine → Feminine tran-
   sition and several percent for other categories in the case of Word2Vec, 1-30% de-
   pending the category for FastText). Moreover, averaging over extremely homony-
   mous prefixes and suffixes makes the results worse (categories A11, A15 for
   FastText over the Araneum corpus).
   Averaging over a word list has some drawbacks. One should have a list of words in
   a given category to average their vectors; this is not always possible. On the other
   hand, sometime such a list is available, and one could use it to tune vectors in order
    Evaluation of Vector Transformations for Russian Word2Vec and FastText Embeddings 11


   to predict out-of-list words. But previously he or she should be sure that this list does
   not contain several preferred semantic directions.
  This list could be used separately, but not for calculating pairs only. Any group will
   have its own center coordinates. If we have a pair a:b, we can use the coordinates of
   the nearest centers instead of the vectors of these words.
3. The main idea of an affine transition is that there is one vector that could be added
   to the word a to find its analogy b. That means that all vectors for a:b should be
   equal, i.e. have approximately equal length and angles of orientation. At least, the
   value of the bias between this transition vector and the vector of the correct answer
   should be less than half the distance to the nearest neighbor. As we have found out,
   it is not always true. In case of homonymous prefixes and suffixes, some vector
   groups could be oppositely directed. This means that the word analogies task could
   not be solved using only one transition vector. Our experiments have demonstrated
   that in some cases the length of the vectors could differ more than twice. Such biases
   lead to the situation, when the software module has to generate several outputs, and
   the user should find some extra methods to find the correct answer.
In our future research, we are going to investigate these drawbacks in more detail. One
of the solutions here is to construct an interpretable vector space where each axis cor-
responds to a semantic feature. LSA-based methods successfully mark domains build-
ing a hierarchical representation of language semantics. However, these methods are
not able to construct a vector space. In our opinion, incorporation of these two methods
(LSA and vector space) could help achieve reasonable results. On the one hand, the
vector space of Word2Vec-inherited methods allows the vector arithmetic in a contin-
uous semantic space; on the other hand, the application of a hierarchy of terms to such
a continuum makes it more interpretable.


References
 1. Bengio, Y., Ducharme, R., Vincent, P., Jauvin, P. A.: Neural Probabilistic Language Model.
    Journal of Machine Learning Research 3, 1137–1155 (2003).
 2. Collobert, R., Weston, J.: A unified architecture for natural language processing. In: Pro-
    ceedings of the 25th International Conference on Machine Learning, vol. 20, pp. 160–167.
    (2008).
 3. Mikolov, T., Yih, W.-T., Zweig, G.: Linguistic Regularities in Continuous Space Word Rep-
    resentations. In: Proc. of HLT-NAACL, pp. 746-751 (2013).
 4. Mikolov, T., Chen, K., Corrado, G., Dean, J.: Efficient estimation of word representations
    in vector space. In: Proc. of International Conference on Learning Representations (ICLR),
    (2013).
 5. Mikolov, T., Chen K., Corrado, G., Dean J.: Distributed Representations of Words and
    Phrases and their Compositionality. In: Proc. of 27th Annual Conference on Neural Infor-
    mation Processing Systems, pp. 3111-3119. (2013).
 6. Bojanowski, P., Grave, E., Joulin, A., Mikolov, T.: Enriching Word Vectors with Subword
    Information. Transactions of the Association for Computational Linguistics 5, 135-146.
    (2017).
12 O. Korogodina, O.Karpik, E. Klyshinsky


 7. Devlin, J., Chang, M., Lee, K., Toutanova, K., BERT: Pre-training of Deep Bidirectional
    Transformers          for        Language          Understanding.          ArXiv:1810.04805,
    https://arxiv.org/pdf/1810.04805.pdf, last accessed 2020/07/12.
 8. Peters, M. E., Neumann, M., Iyyer, M., Gardner, M., Clark, C., Lee, K., Zettlemoyer, L.:
    Deep          contextualized         word         representations.         ArXiv:1802.05365,
    https://arxiv.org/pdf/1802.05365.pdf, last accessed 2020/07/12.
 9. Ethayarajh, K.: How Contextual are Contextualized Word Representations?Comparing the
    Geometry of BERT, ELMo, and GPT-2 Embeddings.                           ArXiv:1909.00512v1,
    https://arxiv.org/pdf/1909.00512.pdf, last accessed 2020/07/12.
10. Levy, O., Goldberg, Y.: Linguistic Regularities in Sparse and Explicit Word Representa-
    tions. In: Proc. of 18th Conf. on Computational Natural Language Learning, pp. 171-180.
    (2014).
11. Köper, M., Scheible, C., Schulte im Walde, S.: Multilingual reliability and “semantic” struc-
    ture of continuous word spaces. In: Proc. of 11th International Conference on Computational
    Semantics, pp. 40–45. (2015)
12. Vylomova, E., Rimmel, L., Cohn, T., Baldwin, T.: Take and took, gaggle and goose, book
    and read: evaluating the utility of vector differences for lexical relation learning. In: Proc.
    of 54th Annual Meeting of the Association for Computational Linguistics, vol. 1, pp. 1671-
    1682. (2016).
13. Rogers, A., Drozd, A., Li, B.: The (Too Many) Problems of Analogical Reasoning with
    Word Vectors. In: Proc. of 6th Joint Conference on Lexical and Computational Semantics,
    pp. 135–148. (2017).
14. Newman-Griffis, D., Lai, A.M., Fosler-Lussier, E.: Insights into analogy completion from
    the biomedical domain. BioNLP, 19-28. (2017).
15. Drozd, A., Gladkova, A., Matsuoka, S.: Analogy-based Detection of Morphological and Se-
    mantic Relations With Word Embeddings: What Works and What Doesn’t. In: Proc. of
    NAACL Student Research Workshop, pp. 8-15. (2016).
16. Linzen, T.: Issues in evaluating semantic spaces using word analogies. In: Proc. of 1st Work-
    shop on Evaluating Vector-Space Representations for NLP, pp. 13–18. (2016).
17. Drozd, A., Gladkova, A., Matsuoka, S.: Word Embeddings, Analogies, and Machine Learn-
    ing: Beyond King-Man+Woman=Queen. In: Proc. of COLING 2016, pp. 3519–3530.
    (2016).
18. Kutuzov, A., Kuzmenko, E.: WebVectors: A Toolkit for Building Web Interfaces for Vector
    Semantic Models. In: Analysis of Images, Social Networks and Texts (AIST) 2016, vol.
    661, pp. 155-161. (2016).
19. Grave, E., Bojanowski, P., Gupta, P., Joulin, A., Mikolov, T.: Learning Word Vectors for
    157 Languages. In: Proc of LREC’2018, pp. 3483-3487. (2018).