trie insert( key, t, depth )
	typekey key;
	trie t;
	int depth;

	{
	int j;
	trie t1;
	if ( t==NULL )	return( NewDataNode(key) );
	if ( IsData(t) )
		if (t->k == key)
			Error /*** Key already in table ***/;
		else {	t1 = NewIntNode();
			t1->p[ charac(depth,t->k) ] = t;
			t = insert( key, t1, depth );
			}
	else  { j = charac(depth,key);
		t->p[j] = insert( key, t->p[j], depth+1 );
		}
	return( t );
	}