******** fig6.55 **********

	PRIORITY_QUEUE
	merge( PRIORITY_QUEUE H1, PRIORITY_QUEUE H2 )
	{
		PRIORITY_QUEUE H3;
		tree_ptr T1, T2, T3;

/*1*/		if( H1 == NULL )
/*2*/			return H2;
/*3*/		if( H2 == NULL )
/*4*/			return H1;
/*5*/		if( H1->rank < H2->rank )
		{
/*6*/			T1 = extract( H1 );	/* extract is a macro */
/*7*/			H3 = merge( H1, H2 );
/*8*/			T1->l_sib = H3->l_sib;
/*9*/			H3->l_sib->r_sib = NULL;
/*10*/			T1->r_sib = H3; H3->l_sib = T1;
/*11*/			return T1;
		}
/*12*/		if( H2->rank < H1->rank )
/*13*/			return merge( H2, H1 );
		/* Otherwise, first two trees have same rank */
/*14*/		T1 = extract( H1 ); T2 = extract( H2 );
/*15*/		H3 = merge( H1, H2 );
/*16*/		T3 = merge_tree( T1, T2 );
/*17*/		return merge( T3, H3 );
	}