invariant - A rule, such as the ordering of an ordered list or heap, that applies throughout the life of a data structure or procedure. Each change to the data structure must maintain the correctness of the invariant.
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дс тдрлими цюлютдажкию дроемжки аиакиохдйис лидр
http://foldoc.doc.ic.ac.uk/foldoc/foldoc.cgi;
