******** fig4.39 **********

	/* This function can be called only if k2 has a left child. */
	/* Perform a rotate between a node (k2) and its left child. */
	/* Update heights */
	/* Then return new root */

	avl_ptr
	s_rotate_left( avl_ptr k2 )
	{
		avl_ptr k1;

		k1 = k2->left;
		k2->left = k1->right;
		k1->right = k2;

		k2->height = max( height(k2->left), height(k2->right) ) + 1;
		k1->height = max( height(k1->left), k2->height ) + 1;

		return k1;		/* New root */
	}