(F=.!arg:0&1|!arg+-1*M$(F$(!arg+-1)));
 (M=.!arg:0&0|!arg+-1*F$(M$(!arg+-1)));

 -1:?n&whl'(!n+1:~>20:?n&put$(F$!n " "))&put$\n
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 -1:?n&whl'(!n+1:~>20:?n&put$(M$!n " "))&put$\n
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