{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T04:04:00Z","timestamp":1760241840131,"version":"build-2065373602"},"reference-count":8,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2018,9,20]],"date-time":"2018-09-20T00:00:00Z","timestamp":1537401600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>In this thesis, we consider the existence of extreme solutions to a class of coupled causal differential equations. By utilizing two comparison theorems and a monotone iterative technique, we have obtained sufficient conditions under which the equations have extreme solutions. One practical example is presented.<\/jats:p>","DOI":"10.3390\/sym10100421","type":"journal-article","created":{"date-parts":[[2018,9,21]],"date-time":"2018-09-21T03:46:35Z","timestamp":1537501595000},"page":"421","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["A Class of Coupled Causal Differential Equations"],"prefix":"10.3390","volume":"10","author":[{"given":"Wen-Li","family":"Wang","sequence":"first","affiliation":[{"name":"Faculty of Fundamental Courses, China University of Geosciences Great Wall College, Baoding 071000, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0631-038X","authenticated-orcid":false,"given":"Jing-Feng","family":"Tian","sequence":"additional","affiliation":[{"name":"College of Science and Technology, North China Electric Power University, Baoding 071051, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Wing-Sum","family":"Cheung","sequence":"additional","affiliation":[{"name":"Department of Mathematics, University of Hong Kong, Pokfulam Road, Hong Kong, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2018,9,20]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1271","DOI":"10.1016\/j.na.2005.06.033","article-title":"Monotone iterative technique for periodic boundary value problems with causal operators","volume":"64","author":"Drici","year":"2006","journal-title":"Nonlinear Anal."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"859","DOI":"10.1016\/j.mcm.2007.11.009","article-title":"Differential equations involving causal operators with nonlinear periodic boundary conditions","volume":"48","author":"Geng","year":"2008","journal-title":"Math. 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