let rec fact n = if n < 2 then 1 else n * (fact (n - 1));;
fact 5;;
#trace fact;;
fact 4;;
#trace Lst.replicate;;
Lst.replicate 4 'z';;
#remove_printer Strng.toplevel_printer;;
Lst.replicate 4 'z';;
#untrace Lst.replicate;;
Strng.from_string "asd";;
Strng.of_string "asd";;
Strng.to_string ['a';'b';'c'];;
#install_printer Strng.toplevel_printer;;
Strng.of_string "asd";;
Lst.foldr1;;
let p= (5, 3, ["*****"; "asdfg"; "*****"]);;
let p= (5, 3, (Lst.map Strng.of_string ["*****"; "asdfg"; "*****"]));;
#remove_printer Picture.toplevel_printer;;
let p= (5, 3, (Lst.map Strng.of_string ["*****"; "asdfg"; "*****"]));;
#install_printer Picture.toplevel_printer;;
let p1 = (5, 1, Strng.of_string "hello");;
let p2 = (5, 1, Strng.of_string "world");;
above
;;
Picture.above;;
Picture.above p1 p2;;
let p2 = (5, 1, [Strng.of_string "world"]);;
let p1 = (5, 1, [Strng.of_string "hello"]);;
Picture.above p1 p2;;
Picture.beside p1 p2;;
Picture.stack;;
Picture.stack [p1;p2;p1;p2;p2];;
foldr1;;
let rec foldr1 f = function
  [] -> failwith "empty"
| [h] -> h
| h :: t -> f h (foldr1 f t);;
foldr1 (+) [2;5;6];;
foldr1 (fun a b -> a ^ " " ^ b) ["qw"; "er"; "ty"];;
Lst.foldr (fun a b -> a ^ " " ^ b) ["qw"; "er"; "ty"] "";;

Picture.pixel;;
Picture.pixel 'h';;
let h = Picture.pixel 'h';;
let e = Picture.pixel 'e';;
Picture.beside h e;;
tile;;
Picture.tile;;
Picture.p00;;
PictureData.p00;;
p00;;
tile;;
open Picture;;
tile;;
tile [[p00; p01; p02]; [p10; p11; p12]];;
empty 5 5;;
#remove_printer Picture.toplevel_printer;;
empty 5 5;;