We present a detailed experimental investigation of the easy-hard-easy phase transition for randomly generated instances of satisfiability problems. Problems in the hard part of the phase transition have been extensively used for benchmarking satisfiability algorithms. This study demonstrates that problem classes and regions of the phase transition previously thought to be easy can sometimes be...

and Introduction: A synthesis of a diverse suite of observations of H2O-related landforms that are possible Mars analogs from terrestrial polar regions (Devon Island in the Arctic; the Dry Va lleys of Antarctica) put into question any requirement for extended episode(s) of warm and wet climate in Mars’s past. Geologically transient episodes of localized H2O cycling, forced by exogenic impacts, ...