@bonifartius likly. kontext is SHA-x . Try to figure out to calculate hash manually on paper. it's a cryptoanarchist thing.
try to understand the checksum of a seedphrase:

function checksum {
result=`cat dice_results|shasum -0 -a 256|cut -c1-2|tr 'a-z' 'A-Z'`
printf 'ibase=16;obase=2;%s\n' "$result"|bc
}

@bonifartius <<<s is left rotation by s bits, <<s left shift by s bits. from some footnote in the book

@begsby what are the boxed +?

@bonifartius dont know, had to stop reading. Me and the author is like Ragnar Lodbrok and Ætheston from vikings. Takes a few seasons