p------------------------------------------------p --l--------------------------------------------l-- ----a----------------------------------------a---- ------i------------------------------------i------ --------n--------------------------------n-------- ----------t----------------------------t---------- ------------e------------------------e------------ --------------x--------------------x-------------- ----------------t----------------t---------------- ------------------ ------------ ------------------ --------------------p--------p-------------------- ----------------------a----a---------------------- ------------------------rr------------------------ -----------------------t--t----------------------- ---------------------y------y--------------------- -------------------l----------l------------------- -----------------i--------------i----------------- ---------------n------------------n--------------- -------------e----------------------e------------- -----------!--------------------------!----------- --------- ------------------------------p--------- -------p----------------------------------l------- -----l--------------------------------------a----- ---a------------------------------------------i--- -i----------------------------------------------n- cross.py