tree merge( a, b )
	tree a, b;

	{
	tree bota, botb, r, temp;
	if ( a==NULL ) return( b );
	else if ( b==NULL ) return( a );
	else	{
		/*** Find bottom of a's rightmost edge ***/
		bota = a->right;	a->right = NULL;
		/*** bottom of b's leftmost edge ***/
		botb = b->left;	b->left = NULL;
		r = NULL;
		/*** Merging loop ***/
		while ( bota!=NULL && botb!=NULL )
			if ( bota->k < botb->k ) {
				temp = bota->right;
				if ( r==NULL )	bota->right = bota;
					else	{bota->right = r->right;
						r->right = bota;
						};
				r = bota;
				bota = temp;
				}
			else	{temp = botb->left;
				if ( r==NULL )	botb->left = botb;
					else	{botb->left = r->left;
						r->left = botb;
						};
				r = botb;
				botb = temp;
				};
		/*** one edge is exhausted, finish merge ***/
		if ( botb==NULL ) {
			a->right = r->right;
			r->right = bota;
			return( a );
			}
		else	{b->left = r->left;
			r->left = botb;
			return( b );
			}
		}
	};