2 |
1. T : Type
2. R : T T Prop
3. k :
4. 0<k
5. x,y:T.
5. (x R^k-1 y)
5. 
5. ( L:T List.
5. (||L|| = k-1+1 & L[0] = x & last(L) = y & ( i: (k-1). L[i] R L[(i+1)]))
x,y:T.
(x if k= 0 x,y. x = y else x,y. z:T. (x R z) & (z R^k-1 y) fi y)

( L:T List.
(||L|| = k+1 & L[0] = x & last(L) = y & ( i: k. L[i] R L[(i+1)]))
 | 23 steps |