Initial data commit

Task/Symmetric-difference/Forth/symmetric-difference.fth

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+: elm	( n -- ; one cell per set )
+	[ cell 8 * 1- ] literal umin CREATE 1 swap lshift ,
+DOES> 	( -- 2^n ) @ ;
+
+: universe	( u "name" -- )
+	dup 0 DO I elm latest swap LOOP
+	CREATE dup , 0 DO , LOOP
+	DOES>  ( n a -- )  dup @ tuck cells +
+		swap 0
+		DO	( n a' )
+			over I rshift 1 AND
+			IF dup @ name>string space type THEN
+			1 cells -
+		LOOP	2drop ;
+
+5 universe john bob mary serena jim	persons
+john bob mary serena or or or
+jim mary john bob    or or or
+
+2dup xor           persons
+2dup -1 xor and cr persons
+swap -1 xor and cr persons
+cr bye