brain-even DEMO: https://asciinema.org/a/55AYd90438QteX4qJtHSroMCW
brain-calc DEMO: https://asciinema.org/a/AB7nAgLmqbECI0JuTSyBPapGT
brain-gcd DEMO: https://asciinema.org/a/COkZw9a7uHD7zWHiVMk8DRgdx
brain-progression DEMO: https://asciinema.org/a/1GTrK3AbKLGL20yaVI6KxTHm5
brain-prime DEMO: https://asciinema.org/a/6FUGL5XWylYbXLJd5VGqjJmp7