; procedures
to square :x
  output :x * :x
end

show defined? "x   ; true
show procedure? "x  ; true (also works for built-in primitives)
erase "x
show defined? "x   ; false
show square 3      ; I don't know how  to square

; names

make "n 23

show name? "n   ; true
ern "n
show name? "n   ; false
show :n     ; n has no value