******** fig4.22 **********

	tree_ptr
	insert( element_type x, SEARCH_TREE T )
	{
/*1*/		if( T == NULL )
		{	/* Create and return a one-node tree */
/*2*/			T = (SEARCH_TREE) malloc ( sizeof (struct tree_node) );
/*3*/			if( T == NULL )
/*4*/				fatal_error("Out of space!!!");
			else
			{
/*5*/				T->element = x;
/*6*/				T->left = T->right = NULL;
			}
		}
		else
/*7*/		if( x < T->element )
/*8*/			T->left = insert( x, T->left );
		else
/*9*/		if( x > T->element )
/*10*/			T->right = insert( x, T->right );
		/* else x is in the tree already.  We'll do nothing */
		
/*11*/		return T;		/* Don't forget this line!! */
	}