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Code in python/ray/rllib/{evolution_strategies, dqn} adapted from
https://github.com/openai (MIT License)

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Code in python/ray/rllib/impala/vtrace.py from
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Copyright 2018 Google LLC

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Code in python/ray/rllib/ars is adapted from https://github.com/modestyachts/ARS

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------------------
Code in python/ray/_private/prometheus_exporter.py is adapted from https://github.com/census-instrumentation/opencensus-python/blob/master/contrib/opencensus-ext-prometheus/opencensus/ext/prometheus/stats_exporter/__init__.py

# Copyright 2018, OpenCensus Authors
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#
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Code in python/ray/tests/modin/test_modin and 
python/ray/tests/modin/modin_test_utils adapted from:
- http://github.com/modin-project/modin/master/modin/pandas/test/test_general.py
- http://github.com/modin-project/modin/master/modin/pandas/test/utils.py

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Code in src/ray/util/logging.h is adapted from 
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