MODULE 	Permute;

FROM	Terminal
IMPORT	Read, Write, WriteLn;

FROM	Terminal2
IMPORT	WriteString;

CONST	MAXIDX = 6;
	MINIDX = 1;

TYPE	TInpCh = ['a'..'z'];
	TChr   = SET OF TInpCh;

VAR	n,
	nl:	INTEGER;
	ch:	CHAR;
	a:	ARRAY[MINIDX..MAXIDX] OF CHAR;
	kt:     TChr = TChr{'a'..'f'};

PROCEDURE output;
VAR	i:	INTEGER;
BEGIN
	FOR i := MINIDX TO n DO Write(a[i]) END;
	WriteString(" | ");
END output;

PROCEDURE exchange(VAR x, y : CHAR);
VAR	z:	CHAR;
BEGIN z := x; x := y; y := z
END exchange;

PROCEDURE permute(k: INTEGER);
VAR	i:	INTEGER;
BEGIN
	IF k = 1 THEN
		output;
		INC(nl);
		IF (nl MOD 8 = 1) THEN WriteLn END;
	ELSE
		permute(k-1);
		FOR i := MINIDX TO k-1 DO
			exchange(a[i], a[k]);
			permute(k-1);
			exchange(a[i], a[k]);
		END
	END
END permute;

BEGIN
	n := 0;	nl := 1; WriteString("Input {a,b,c,d,e,f} >");
	REPEAT
		Read(ch);
		IF ch IN kt THEN INC(n); a[n] := ch; Write(ch) END
	UNTIL (ch <= " ") OR (n > MAXIDX);

	WriteLn;
	IF n > 0 THEN permute(n) END;
	(*Wait*)
END Permute.