function f/0
  assumption
  end assumption
end function

# (function (@ 1 0-8) ‘f/0’
#   (.inner
#     (assumption (@ 2 2-12)
#       (.inner nil)
#     )
#   )
# )
# :2:2–12: error: assumption clause inside function definition
#    assumption
#    ^^^^^^^^^^
# :1:0–8: note: outer function definition defined here
#  function f/0
#  ^^^^^^^^