		/**** Permutations: list arrangements of a set  ****/

mode none.	
closure  none.

perms(phi)   contains {[]}.
perms({X\T}) contains distr(X, perms(T)).  % absence of mode info means 
					   % perms(T) will produce *all*
					   % permutations of T
	distr(X, {H\_}) contains {[X|H]}.
