We present in this paper the KO library, which calculates an analytic decomposition of the Yukawa interactions invariant under SO(2N) in terms of an SU(N) basis. We make use of the oscillator expansion formalism, where the SO(2N) spinor representations are expressed in terms of creation and annihilation operators of a Grassmann algebra acting on a vacuum state. These noncommutative operators and their products are simulated in SOSpin through the implementation of doubly-linked-list data structures. These data structures were determinant to achieve a higher performance in the simplification of large products of creation and annihilation operators. We illustrate the use of our library with complete examples of how to decompose Yukawa terms invariant under SO(2N) in terms of SU(N) degrees of freedom for N = 2 and 5. We further demonstrate, with an example for SO(4), that higher dimensional field-operator terms can also be processed with our library. Finally, we describe the functions available in SE that are made to simplify the writing of spinors and their interactions specifically for SO(10) models. Program summary Program title: SOSpin Catalogue identifier: AEZM_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEZM_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License, version 3 No. of lines in distributed program, including test data, etc.: 25623 No. of bytes in distributed program, including test data, etc.: 200391 Distribution format: tar.gz Programming, language: C++. Computer: PC, Apple. Operating system: UNIX (Linux, Mac OS X 11). RAM: >20 MB depending on the number of processes required Classification: 4.2, 11.1, 11.6. External routines: In order to make further simplifications on the expressions obtained the library calls the Symbolic Manipulation System FORM program [1]. Nature of problem: The decomposition of an Yukawa interaction invariant under SO(2N) in terms of SU (N) fields. Solution method: We make use of the oscillator expansion formalism, where the SO(2N) spinor representations are expressed in terms of creation and annihilation operators of a Grassmann algebra acting on a vacuum state. Running time: It depends on the input expressions, it can take a few seconds or more for very large representations (because of memory exhaustion). (C) 2016 Elsevier B.V. All rights reserved.