rem: penter(p)	 Node *p;
add: penter(Node *p)
context: penter(p)	/* set up parent pointers and leaf indices */	Node *p;{	switch(type(p)) {	LEAF		left(p) = (Node *) poscnt;		point[poscnt++] = p;		break;	UNARY		penter(left(p));		parent(left(p)) = p;		break;	case CAT:	case OR:		penter(left(p));		penter(right(p));		parent(left(p)) = p;		parent(right(p)) = p;		break;	default:		ERROR "unknown type %d in penter", type(p) FATAL;		break;	}}