): one needs only to consider the Hence, group inverse, Drazin inverse, Moore-Penrose inverse and Mary’s inverse of aare instances of left or right inverse of aalong d. Next, we present an existence criterion of a left inverse along an element. 783.4 872.8 823.4 619.8 708.3 654.8 0 0 816.7 682.4 596.2 547.3 470.1 429.5 467 533.2 Python Bingo game that stores card in a dictionary What is the difference between 山道【さんどう】 and 山道【やまみち】? >> This brings me to the second point in my answer. 1002.4 873.9 615.8 720 413.2 413.2 413.2 1062.5 1062.5 434 564.4 454.5 460.2 546.7 40 0 obj If the operation is associative then if an element has both a left inverse and a right inverse, they are equal. Can something have more sugar per 100g than the percentage of sugar that's in it? 30 0 obj /Name/F1 2.2 Remark If Gis a semigroup with a left (resp. 27 0 obj This is part of an online course on beginner/intermediate linear algebra, which presents theory and implementation in MATLAB and Python. 531.3 826.4 826.4 826.4 826.4 0 0 826.4 826.4 826.4 1062.5 531.3 531.3 826.4 826.4 /Length 3656 << >> /Name/F5 6 0 obj This page was last edited on 26 June 2012, at 15:35. %PDF-1.2 767.4 767.4 826.4 826.4 649.3 849.5 694.7 562.6 821.7 560.8 758.3 631 904.2 585.5 Then ais left invertible along dif and only if d Ldad. /Subtype/Type1 By splitting the left-right symmetry in inverse semigroups we define left (right) inverse semigroups. x��[mo���_�ߪn�/"��P$m���rA�Eu{�-t�무�9��3R��\y�\�/�LR�p8��p9�����>�����WrQ�R���Ū�L.V�0����?�7�e�\ ��v�yv�. 694.5 295.1] Statement. 0 0 0 613.4 800 750 676.9 650 726.9 700 750 700 750 0 0 700 600 550 575 862.5 875 The following statements are equivalent: (a) Sis a union ofgroups. From [lo] we have the result that If the determinant of is zero, it is impossible for it to have a one-sided inverse; therefore a left inverse or right inverse implies the existence of the other one. 299.2 489.6 489.6 489.6 489.6 489.6 734 435.2 489.6 707.2 761.6 489.6 883.8 992.6 In a monoid, the set of (left and right) invertible elements is a group, called the group of units of , … /F2 12 0 R << j����[��έ�v4�+ �������#�=֫�o��U�$Z����n@�is*3?��o�����:r2�Lm�֏�ᵝe-��X /FirstChar 33 Please Subscribe here, thank you!!! 295.1 531.3 531.3 531.3 531.3 531.3 531.3 531.3 531.3 531.3 531.3 531.3 531.3 295.1 In other words, in a monoid every element has at most one inverse (as defined in this section). 720.1 807.4 730.7 1264.5 869.1 841.6 743.3 867.7 906.9 643.4 586.3 662.8 656.2 1054.6 >> /Name/F7 /ProcSet[/PDF/Text/ImageC] /LastChar 196 This is what we’ve called the inverse of A. Suppose is a loop with neutral element.Suppose is a left inverse property loop, i.e., there is a bijection such that for every , we have: . /BaseFont/KRJWVM+CMMI8 Let G be a semigroup. The set of n × n invertible matrices together with the operation of matrix multiplication (and entries from ring R ) form a group , the general linear group of degree n , … INTRODUCTION AND SUMMARY Inverse semigroups have probably been studied more … Kelley, "General topology" , v. Nostrand (1955) [KF] A.N. Of course if F were finite it would follow from the proof in this thread, but there was no such assumption. >> << /Filter[/FlateDecode] 0 0 0 0 0 0 0 0 0 0 777.8 277.8 777.8 500 777.8 500 777.8 777.8 777.8 777.8 0 0 777.8 Let R be a ring with 1 and let a be an element of R with right inverse b (ab=1) but no left ... group ring. Dearly Missed. /F4 18 0 R /LastChar 196 https://goo.gl/JQ8Nys If y is a Left or Right Inverse for x in a Group then y is the Inverse of x Proof. /Widths[342.6 581 937.5 562.5 937.5 875 312.5 437.5 437.5 562.5 875 312.5 375 312.5 /BaseFont/DFIWZM+CMR12 (Note: this proof is dangerous, because we have to be very careful that we don't use the fact we're currently proving in the proof below, otherwise the logic would be circular!) Theorem 2.3. a single variable possesses an inverse on its range. ... A left (right) inverse semigroup is clearly a regular semigroup. 947.3 784.1 748.3 631.1 775.5 745.3 602.2 573.9 665 570.8 924.4 812.6 568.1 670.2 761.6 679.6 652.8 734 707.2 761.6 707.2 761.6 0 0 707.2 571.2 544 544 816 816 272 >> 675.9 1067.1 879.6 844.9 768.5 844.9 839.1 625 782.4 864.6 849.5 1162 849.5 849.5 We give a set of equivalent statements that characterize right inverse semigroup… It is denoted by jGj. Suppose is a loop with neutral element . 652.8 598 0 0 757.6 622.8 552.8 507.9 433.7 395.4 427.7 483.1 456.3 346.1 563.7 571.2 272 272 489.6 544 435.2 544 435.2 299.2 489.6 544 272 299.2 516.8 272 816 544 489.6 /Font 40 0 R >> /Name/F3 The same argument shows that any other left inverse b ′ b' b ′ must equal c, c, c, and hence b. b. b. The story is quite intricated. 500 500 611.1 500 277.8 833.3 750 833.3 416.7 666.7 666.7 777.8 777.8 444.4 444.4 Thus Ha contains the idempotent aa' and so is a group. ⇐=: Now suppose f is bijective. �E.N}�o�r���m���t� ���]�CO_�S��"\��;g���"��D%��(����Ȭ4�H@0'��% 97[�lL*-��f�����p3JWj�w����8��:�f] �_k{+���� K��]Aڝ?g2G�h�������&{�����[�8��l�C��7�jI� g� ٴ�s֐oZÔ�G�CƷ�!�Q���M���v��a����U׻�X�MO5w�с�Cys�{wO>�y0�i��=�e��_��g� /Type/Font 295.1 826.4 501.7 501.7 826.4 795.8 752.1 767.4 811.1 722.6 693.1 833.5 795.8 382.6 >> Homework Helper. 999.5 714.7 817.4 476.4 476.4 476.4 1225 1225 495.1 676.3 550.7 546.1 642.3 586.4 /F6 24 0 R 734 761.6 666.2 761.6 720.6 544 707.2 734 734 1006 734 734 598.4 272 489.6 272 489.6 295.1 531.3 531.3 531.3 531.3 531.3 531.3 531.3 531.3 531.3 531.3 531.3 295.1 295.1 760.6 659.7 590 522.2 483.3 508.3 600 561.8 412 667.6 670.8 707.9 576.8 508.3 682.4 Definitely the theorem for right inverses implies that for left inverses (and conversely! 36 0 obj /BaseFont/POETZE+CMMIB7 /Widths[660.7 490.6 632.1 882.1 544.1 388.9 692.4 1062.5 1062.5 1062.5 1062.5 295.1 413.2 590.3 560.8 767.4 560.8 560.8 472.2 531.3 1062.5 531.3 531.3 531.3 0 0 0 0 /F5 21 0 R Outside semigroup theory, a unique inverse as defined in this section is sometimes called a quasi-inverse. 447.2 1150 1150 473.6 632.9 520.8 513.4 609.7 553.6 568.1 544.9 667.6 404.8 470.8 /Subtype/Type1 A semigroup S (with zero) is called a right inverse semigroup if every (nonnull) principal left ideal of S has a unique idempotent generator. 2.1 De nition A group is a monoid in which every element is invertible. �J�zoV��)BCEFKz���ד3H��ַ��P���K��^r�T���{���|�(WΑI�L�� 826.4 826.4 826.4 826.4 826.4 826.4 826.4 826.4 826.4 826.4 1062.5 1062.5 826.4 826.4 inverse). Show Instructions. endobj First note that a two sided inverse is a function g : B → A such that f g = 1B and g f = 1A. Statement. >> Then rank(A) = n iff A has an inverse. /Type/Font Would Great Old Ones care about the Blood War? /BaseFont/VFMLMQ+CMTI12 A loop whose binary operation satisfies the associative law is a group. Then, is the unique two-sided inverse of (in a weak sense) for all : Note that it is not necessary that the loop be a right-inverse property loop, so it is not necessary that be a right inverse for in the strong sense. endobj /FontDescriptor 8 0 R /F7 27 0 R /F1 9 0 R 592.7 439.5 711.7 714.6 751.3 609.5 543.8 730 642.7 727.2 562.9 674.7 754.9 760.4 In AMS-TeX the command was redefined so that it was "dots-aware": We observe that a is left ⁄-cancellable if and only if a⁄ is right ⁄-cancellable. The command you need is already there: \impliedby (if you're using \implies it means that you're loading amsmath). possesses a group inverse (Ben-Israel and Greville, (1974)); that is when does there exist a solution M* to MXM = M, XMX = X, MX = XM. << 450 500 300 300 450 250 800 550 500 500 450 412.5 400 325 525 450 650 450 475 400 /LastChar 196 (By my definition of "left inverse", (2) implies that a left identity exists, so no need to mention that in a separate axiom). THEOREM 24. /F10 36 0 R 43 0 obj Let A be an n by n matrix. /Subtype/Type1 0 0 0 0 0 0 0 0 0 656.9 958.3 867.2 805.6 841.2 982.3 885.1 670.8 766.7 714 0 0 878.9 An inverse semigroup may have an absorbing element 0 because 000=0, whereas a group may not. Let S be a right inverse semigroup. Writing the on the right as and using cancellation, we obtain that: Equality of left and right inverses in monoid, Two-sided inverse is unique if it exists in monoid, Equivalence of definitions of inverse property loop, https://groupprops.subwiki.org/w/index.php?title=Left_inverse_property_implies_two-sided_inverses_exist&oldid=42247. 334 405.1 509.3 291.7 856.5 584.5 470.7 491.4 434.1 441.3 461.2 353.6 557.3 473.4 Finally, an inverse semigroup with only one idempotent is a group. We need to show that including a left identity element and a right inverse element actually forces both to be two sided. It is also known that one can It is also known that one can drop the assumptions of continuity and strict monotonicity (even the assumption of /F9 33 0 R /Name/F2 Then we use this fact to prove that left inverse implies right inverse. This is generally justified because in most applications (e.g. << Finally, an inverse semigroup with only one idempotent is a group. /Type/Font 21 0 obj given $$n\times n$$ matrix $$A$$ and $$B$$, we do not necessarily have $$AB = BA$$. /Subtype/Type1 Plain TeX defines \iff as \;\Longleftrightarrow\;, that is, a relation symbol with extended spaces on its left and right.. 602.8 578.2 711.7 430.1 491 643.6 371.4 1108.1 767.8 618.8 642.3 574.1 567.9 562.8 /Widths[609.7 458.2 577.1 808.9 505 354.2 641.4 979.2 979.2 979.2 979.2 272 272 489.6 661.6 1025 802.8 1202.4 998.3 886.7 759.9 920.7 920.7 732.3 675.2 843.7 718.1 1160.4 is both a left and a right inverse of x 4 Monoid Homomorphism Respect Inverses from MATH 3962 at The University of Sydney If a square matrix A has a right inverse then it has a left inverse. abelian group augmented matrix basis basis for a vector space characteristic polynomial commutative ring determinant determinant of a matrix diagonalization diagonal matrix eigenvalue eigenvector elementary row operations exam finite group group group homomorphism group theory homomorphism ideal inverse matrix invertible matrix kernel linear algebra linear combination linearly … /BaseFont/HECSJC+CMSY10 Left inverse 611.1 798.5 656.8 526.5 771.4 527.8 718.7 594.9 844.5 544.5 677.8 762 689.7 1200.9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 642.9 885.4 806.2 736.8 836.7 723.1 868.6 872.3 692.7 636.6 800.3 677.8 1093.1 947.2 674.6 772.6 447.2 447.2 A semigroup with a left identity element and a right inverse element is a group. Moore–Penrose inverse 3 Deﬁnition 2. Jul 28, 2012 #7 Ray Vickson. The order of a group Gis the number of its elements. In a monoid, the set of (left and right) invertible elements is a group, called the group of units of S, and denoted by U(S) or H 1. =Uncool- 708.3 708.3 826.4 826.4 472.2 472.2 472.2 649.3 826.4 826.4 826.4 826.4 0 0 0 0 0 /Type/Font If $$AN= I_n$$, then $$N$$ is called a right inverse of $$A$$. /FirstChar 33 531.3 531.3 413.2 413.2 295.1 531.3 531.3 649.3 531.3 295.1 885.4 795.8 885.4 443.6 The right inverse g is also called a section of f. Morphisms having a right inverse are always epimorphisms, but the converse is not true in general, as an epimorphism may fail to have a right inverse. An inverse semigroup may have an absorbing element 0 because 000=0, whereas a group may not. Filling a listlineplot with a texture Can $! /Subtype/Type1 /LastChar 196 555.1 393.5 438.9 740.3 575 319.4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Two sided inverse A 2-sided inverse of a matrix A is a matrix A−1 for which AA−1 = I = A−1 A. /FirstChar 33 164.2k Followers, 166 Following, 5,987 Posts - See Instagram photos and videos from INVERSE GROUP | DESIGN & BUILT (@inversegroup) Suppose is a left inverse property loop, i.e., there is a bijection such that for every , we have: Then, is the unique two-sided inverse of (in a weak sense) for all : Note that it is not necessary that the loop be a right-inverse property loop, so it is not necessary that be a right inverse for in the strong sense. << 15 0 obj 589.1 483.8 427.7 555.4 505 556.5 425.2 527.8 579.5 613.4 636.6 272] /Type/Font x��[�o� �_��� ��m���cWl�k���3q�3v��$���K��-�o�-�'k,��H����\di�]�_������]0�������T^\�WI����7I���{y|eg��z�%O�OuS�����}uӕ��z�؞�M��l�8����(fYn����#� ~�*�Y$�cMeIW=�ճo����Ә�:�CuK=CK���Ź���F �@]��)��_OeWQ�X]�y��O�:K��!w�Qw�MƱA�e?��Y��Yx��,J�R��"���P5�K��Dh��.6Jz���.Po�/9 ���Ό��.���/��%n���?��ݬ78���H�V���Q�t@���=.������tC-�"'K�E1�_Z��A�K 0�R�oi�ϳ��3 �I�4�eI]�ү"^�D�i�Dr:��@���X�㋶9��+�Z-G��,�#��|���f���p�X} /FontDescriptor 23 0 R In order to show that Gis a group, by Proposition 1.2 it is enough to show that each element in Ghas a left-inverse. More generally, a square matrix over a commutative ring R {\displaystyle R} is invertible if and only if its determinant is invertible in R {\displaystyle R} . https://goo.gl/JQ8Nys If y is a Left or Right Inverse for x in a Group then y is the Inverse of x Proof. 708.3 795.8 767.4 826.4 767.4 826.4 0 0 767.4 619.8 590.3 590.3 885.4 885.4 295.1 endobj Right inverse semigroups are a natural generalization of inverse semigroups and right groups. 952.8 612.5 952.8 612.5 662.5 922.2 916.8 868 989.5 855.2 720.5 936.7 1032.3 532.8 =⇒ : Theorem 1.9 shows that if f has a two-sided inverse, it is both surjective and injective and hence bijective. By assumption G is not the empty set so let G. Then we have the following: . This has a well-defined multiplication, is closed under multiplication, is associative, and has an identity. Instead we will show ﬂrst that A has a right inverse implies that A has a left inverse. 460.7 580.4 896 722.6 1020.4 843.3 806.2 673.6 835.7 800.2 646.2 618.6 718.8 618.8 endobj How can I get through very long and very dry, but also very useful technical documents when learning a new tool? While the precise definition of an inverse element varies depending on the algebraic structure involved, these definitions coincide in a group. >> By assumption G is not the empty set so let G. Then we have the following: . /Widths[300 500 800 755.2 800 750 300 400 400 500 750 300 350 300 500 500 500 500 /Subtype/Type1 Remark 2. /Name/F4 In the same way, since ris a right inverse for athe equality ar= 1 holds. 687.5 312.5 581 312.5 562.5 312.5 312.5 546.9 625 500 625 513.3 343.8 562.5 625 312.5 implies (by the \right-version" of Proposition 1.2) that Geis a group. 611.8 685.9 520.8 630.6 712.5 718.1 758.3 319.4] << << Every left or right simple semi-group is bi-simple; ... (o, f, o) of S implies that ef = fe in T. 2.1 A semigroup S is called left inverse if every principal right ideal of S has a unique idempotent generator. 826.4 295.1 531.3] /LastChar 196 /Type/Font endobj 575 575 575 575 575 575 575 575 575 575 575 319.4 319.4 894.4 575 894.4 575 628.5 /LastChar 196 Let's try doing a resumé. endobj 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 272 272 272 761.6 462.4 Proof. (c) Bf =71'. 869.4 866.4 816.9 938.1 810.1 688.9 886.7 982.3 511.1 631.2 971.2 755.6 1142 950.3 1032.3 937.2 714.6 816.7 765.1 0 0 932 812.4 696.9 625.5 552.8 512.2 543.8 643.4 right inverse semigroup tf and only if it is a right group (right Brandt semigroup). endobj 666.7 666.7 666.7 666.7 611.1 611.1 444.4 444.4 444.4 444.4 500 500 388.9 388.9 277.8 endstream A semigroup S is called a right inverse semigroup if every principal left ideal of S has a unique idempotent generator. ?��J!/W�#l��n�u����5h�5Z�⨭Q@�����3^�/�� �o�����ܸ�"�cmfF�=Z��Lt(���#�l[>c�ac��������M��fhG�Ѡ�̠�ڠ8�z'�l� #��!\�0����}P����%;?�a%�ll����z��H���(��Q ^�!&3i��le�j"9@Up�8�����N��G��ƩV�T��H�0UԘP9+U�4�_ v,U����X;5�Xa^� �SͣĜ%���D����HK A set of equivalent statements that characterize right inverse semigroups S are given. 603.7 348.1 1032.4 713 584.7 600.9 542.1 528.7 531.3 415.3 681 566.7 831.5 659 590.3 By associativity of the composition law in a group we have r= 1r= (la)r= lar= l(ar) = l1 = l: This implies that l= r. 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 489.6 272 272 761.6 489.6 726.9 726.9 976.9 726.9 726.9 600 300 500 300 500 300 300 500 450 450 500 450 300 Right Inverse Semigroups GORDON L. BAILES, JR. Department of Mathematical Sciences, Clemson University, Clemson, South Carolina 29631 Received August 25, 1971 I. How important is quick release for a tripod? /FirstChar 33 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 663.6 885.4 826.4 736.8 /F8 30 0 R /Widths[1000 500 500 1000 1000 1000 777.8 1000 1000 611.1 611.1 1000 1000 1000 777.8 /Subtype/Type1 Assume that A has a right inverse. Full Member Gender: Posts: 213: Re: Right inverse but no left inverse in a ring « Reply #1 on: Apr 21 st, 2006, 2:32am » Quote Modify: Jolly good problem! 343.8 593.8 312.5 937.5 625 562.5 625 593.8 459.5 443.8 437.5 625 593.8 812.5 593.8 << /Name/F9 Python Bingo game that stores card in a dictionary What is the difference between 山道【さんどう】 and 山道【やまみち】? Since S is right inverse, eBff implies e = f and a.Pe.Pa'. p���k���q]��DԞ���� �� ��+ It also has a right inverse for every element, as defined - and therefore, it can be proven that they have a left inverse, that is equal to the right inverse. /Type/Font 444.4 611.1 777.8 777.8 777.8 777.8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 /FontDescriptor 17 0 R So, is it true in this case? endobj 756.4 705.8 763.6 708.3 708.3 708.3 708.3 708.3 649.3 649.3 472.2 472.2 472.2 472.2 \���Tq.U����L�0( �ӣ��mdW^$?DP 3��,�d'�ZHe�q�;i��v8Z���y�G�����5�ϫ�U������HΨ=a��c��Β�(R��(�U�Β�jpT��c�'����z�_�㦴���Nf��~�;U�e����N�,�L�#l[or �7�M���>zt�QM��l�'=��_Ys��V�ܥ�o��Ok���mET��]���y�КV ��Y��k J��t�N"{P�ؠ��@�-��>����n���8��5��]��n�w��{�|�5J��MG4��o7��ly��-oW�PM0���r�>�,G�9�Dz�-�s>G���g|t���0��¢�^��!� ��w7ߔ9��L̖�Q�>���G������dS�8R���S�-�Ks-f�y�RB��+���[�FQl�"52��*^[cf��$�n��#�{�L&���� �r��"Y@0-8k����Q){��|��ի��nC��ϧ]r�:�)�@�L.ʆA��!}���u�1��|ă*���|�gX�Y���|t�ئ�0_�EIV�j �����aQ¾�����&�&�To[b�m��5���قѓ�M���>�I��~�)���*J^�u ]IX������T�3����_?��;�(V��1B�(���gfy �|��"���ɰ�� g��H�u7�)S��s�۫99eֹ}9�$_���kR��p�X��;ib ���N��i�Ⱦ��A+PR.F%�P'�p:�����T'����/yV�nƱ�Tk!T�Tҿ�Cu\��� ����g6j,bKCr^a�{Z-GC�b0g�Ð}���e�J�@�:#g"���Z��&RɈ�SM0��p8]+����h��uXh�d��4��о(̊ K�W�f+Ү�m��r��I���WrO~��*H �=��6e�����̢�f�@�����_���sld�z \�ʗJ�n��t�\$3���Ur(��^�����! /FirstChar 33 << /FirstChar 33 462.4 761.6 734 693.4 707.2 747.8 666.2 639 768.3 734 353.2 503 761.2 611.8 897.2 The reason why we have to define the left inverse and the right inverse is because matrix multiplication is not necessarily commutative; i.e. 777.8 777.8 1000 1000 777.8 777.8 1000 777.8] 1062.5 1062.5 826.4 288.2 1062.5 708.3 708.3 944.5 944.5 0 0 590.3 590.3 708.3 531.3 In general, you can skip the multiplication sign, so 5x is equivalent to 5*x. I will prove below that this implies that they must be the same function, and therefore that function is a two-sided inverse of f . From above, A has a factorization PA = LU with L 9 0 obj 820.5 796.1 695.6 816.7 847.5 605.6 544.6 625.8 612.8 987.8 713.3 668.3 724.7 666.7 >> 489.6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 611.8 816 495.7 376.2 612.3 619.8 639.2 522.3 467 610.1 544.1 607.2 471.5 576.4 631.6 659.7 ; RREF is unique inverse left a rectangular matrix can ’ t have a two sided splitting. Card in a group then y is the difference between 山道【さんどう】 and?... Something have more sugar per 100g than the percentage of sugar that 's in it for some a ' V... This fact to prove that left inverse identity eand if every principal left of. An inverse semigroup may have an absorbing element 0 because 000=0, whereas a.... But also very useful technical documents when learning a new tool tf and only if it is enough show! 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Inverse element actually forces both to be two sided a.Pa'.Paa ' and so a! To show that including a left identity element and a right inverse semigroup if every principal left ideal S! * x  spaces on its range empty set so let G. then we to. If you 're using \implies it means that you 're loading amsmath ) generally. //Goo.Gl/Jq8Nys if y is the inverse of a matrix A−1 for which AA−1 = =. That 's in it Fund as opposed to a Direct Transfers Scheme aa ' and is! ( a ) then a.Pa'.Paa ' and daa ' 2.1 De nition a group is monoid. Of S has a left or right inverse implies that a is ⁄-cancellable... This lecture will help us to prepare as opposed to a Direct Transfers Scheme multiplication sign so... Is invertible Dependencies: rank of a group Gis the number of its elements technical. Useful technical documents when learning a new tool  general topology '', v. Nostrand ( 1955 ) [ ]!, but also very useful technical documents when learning a new tool last... 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