Add to ORKGLink to publication Citation for published version (APA): Liu, L. (1993). A formal approach to structure, algebra & communication of complex objects [s.l.]: [s.n.] General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.? Users may download and print one copy of any publication from the public portal for the purpose of private study or research? You may not further distribute the material or use it for any profit-making activity or commercial gain? You may freely distribute the URL identifying the publica...