pop =: ( {.^:notnull ; }. )@: > @: ] /
push =: ( '' ; ,~ )& > /
tell_atom =: >& {.
tell_queue =: >& {:
is_empty =: '' -: 1 tell_queue
make_empty =: a: , a: [ ]
onto =: [ ; }.@]
notnull =: 0 ~: #