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[Conway 05] pg. 360 "Inheritance"
[CPAN] Shank, Elliot, Perl-Critic-1.116 ClassHierarchies::ProhibitExplicitISA
[CPAN] Dolan, Chris. base [CPAN] Garcia-Suarez, Rafaël, Lateur, Bart, Maischein, Max, Siegel, Anno, Schwern, Michael parent
02. Expressions EXP31-PL. Do not use the two-argument form of open()