* lib/Automake/ConditionalSet.pm (conds): Use value() to simplify. (invert): Rewrite as a product-of-sums to sum-of-products converter. (_multiply, multiply): New functions. * lib/Automake/Conditional.pm (not): New function. * lib/Automake/tests/ConditionalSet.pl (test_invert): Update. * automake.in (condition_negate): Move ... * lib/Automake/Conditional.pm (negate_condition): ... here. Suggested by Raja R Harinath.