to longest :s :t
  output ifelse greater? count :s count :t [:s] [:t]
end
to lcs :s :t
  if empty? :s [output :s]
  if empty? :t [output :t]
  if equal? first :s first :t [output combine  first :s  lcs bf :s bf :t]
  output longest lcs :s bf :t  lcs bf :s :t
end