Paywalls and membership only databases are annoying. One obstacle has been temporarily removed: The Association for Computing Machinery (ACM) announces: "To help support our community working remotely during COVID-19, we are making all work published by ACM in our Digital Library freely accessible through June 30, 2020." e.g. http://dl.acm.org/citation.cfm?doid=307824.307853 -- on MindForth AI -- is now freely accessible to read or download as a Portable Document FIle (PDF).