to about :a :b
  output and [:a - :b < 1e-15] [:a - :b > -1e-15]
end
to agm :arith :geom
  if about :arith :geom [output :arith]
  output agm (:arith + :geom)/2  sqrt (:arith * :geom)
end

show agm 1 1/sqrt 2