2. P : L:(T List)
(||L||-1)
3. m : (T List)
4.
L:T List, i:(||L||-1).
4. P(L,i)
P(swap(L;i;i+1),i) & m(swap(L;i;i+1))<m(L)
5. L : T List
6. 0<||L||
7. f : (T List)
(T List)
8.
L:T List.
8. f(L)
8. =
8. if null(L)
L
8. else let i = search(||L||-1;P(L)) in if i=
0 L else swap(L;i-1;i) fi fi
9.
x:T List. 
n:. f(f^n(x)) = f^n(x)
10. n :
11. 0<n
12. L guarded_permutation(T;
L,i. P(L,i)) (f^n-1(L))
13. Trans x,y:T List. x guarded_permutation(T;
L,i. P(L,i)) y
f^n(L) = f(f^n-1(L))
