let A = "ACGTACGTACGT"
and B = "ACTAGCTACTGT"

in let
LCS A B =
   let rec
       down []       _ _ = nil  ||
       down (Ach.As) B L =
          let rec
              across []       _    _     _     = nil  ||           -- NW N
              across (Bch.Bs) West NWest North =                   -- W  here
                 (if Ach=Bch then (1+hd NWest) else max (hd West) (hd North) )
               . across Bs (tl West) (tl NWest) (tl North)

          and thisrow = 0 . across B thisrow (hd L) (tl(hd L))

          in  thisrow . down As B (tl L)

   and L = (0. map (\x.0) B)   -- [ [0; 0; 0; ...; 0] ;
                 . down A B L  --   [0; ...         ] ;
                               --   ... ]
in last(last L)

in "LCS(" @ A @ ", " @ B @ ") = " @ itos( LCS A B )

--\fB O(|A|*|B|) Longest Common Subsequence Algorithm. \fP