* lib/Automake/ConditionalSet.pm (_simplify, simplify): New methods. (true): Cache return value, so _simplify can use it. * lib/Automake/tests/ConditionalSet.pl (test_simplify): New function. * automake.in (variable_not_always_defined_in_cond): Return a simplified ConditionalSet. (macro_define, require_variables): Adjust. * tests/Makefile.am (TEST): Add library3.test. * tests/library3.test: New file. * tests/pluseq9.test: Adjust. Thanks to Raja R Harinath.