switch (BASIC(a1)->id) {
	case ID_ADD:
	  {
	    COUNTUP_INTERACTION(vm);
	    
	    BASIC(a1)->id = ID_ADD2;
	    VALUE a1port1 = AGENT(a1)->port[1];
	    AGENT(a1)->port[1] = a2;
	    a2 = a1port1;
	    goto loop;
	  }
	case ID_ADD2:
	  {
	    COUNTUP_INTERACTION(vm);
	    
	    // r << Add(m,n)
	    long n = FIX2INT(AGENT(a1)->port[1]);
	    long m = FIX2INT(a2);
	    a2 = INT2FIX(m+n);
	    VALUE a1port0 = AGENT(a1)->port[0];
	    free_Agent(a1);
	    a1 = a1port0;
	    goto loop;
	  }
	case ID_SUB:
	  {
	    COUNTUP_INTERACTION(vm);
	    
	    BASIC(a1)->id = ID_SUB2;
	    VALUE a1port1 = AGENT(a1)->port[1];
	    AGENT(a1)->port[1] = a2;
	    a2 = a1port1;
	    goto loop;
	  }
	case ID_SUB2:
	  {	    
	    COUNTUP_INTERACTION(vm);
	    
	    // r << Sub(m,n)
	    long n = FIX2INT(AGENT(a1)->port[1]);
	    long m = FIX2INT(a2);
	    a2 = INT2FIX(m-n);
	    VALUE a1port0 = AGENT(a1)->port[0];
	    free_Agent(a1);
	    a1 = a1port0;
	    goto loop;
	  }
	case ID_MUL:
	  {
	    COUNTUP_INTERACTION(vm);
	    
	    BASIC(a1)->id = ID_MUL2;
	    VALUE a1port1 = AGENT(a1)->port[1];
	    AGENT(a1)->port[1] = a2;
	    a2 = a1port1;
	    goto loop;
	  }
	case ID_MUL2:
	  {
	    COUNTUP_INTERACTION(vm);
	    
	    // r << Mult(m,n)
	    long n = FIX2INT(AGENT(a1)->port[1]);
	    long m = FIX2INT(a2);
	    a2 = INT2FIX(m*n);
	    VALUE a1port0 = AGENT(a1)->port[0];
	    free_Agent(a1);
	    a1 = a1port0;
	    goto loop;
	  }
	case ID_DIV:
	  {
	    COUNTUP_INTERACTION(vm);
	    
	    BASIC(a1)->id = ID_DIV2;
	    VALUE a1port1 = AGENT(a1)->port[1];
	    AGENT(a1)->port[1] = a2;
	    a2 = a1port1;
	    goto loop;
	  }
	case ID_DIV2:
	  {
	    COUNTUP_INTERACTION(vm);
	    
	    // r << DIV(m,n)
	    long n = FIX2INT(AGENT(a1)->port[1]);
	    long m = FIX2INT(a2);
	    a2 = INT2FIX(m/n);
	    VALUE a1port0 = AGENT(a1)->port[0];
	    free_Agent(a1);
	    a1 = a1port0;
	    goto loop;
	  }
	case ID_MOD:
	  {
	    COUNTUP_INTERACTION(vm);
	    
	    BASIC(a1)->id = ID_MOD2;
	    VALUE a1port1 = AGENT(a1)->port[1];
	    AGENT(a1)->port[1] = a2;
	    a2 = a1port1;
	    goto loop;
	  }
	case ID_MOD2:
	  {
	    COUNTUP_INTERACTION(vm);
	    
	    // r << MOD(m,n)
	    long n = FIX2INT(AGENT(a1)->port[1]);
	    long m = FIX2INT(a2);
	    a2 = INT2FIX(m%n);
	    VALUE a1port0 = AGENT(a1)->port[0];
	    free_Agent(a1);
	    a1 = a1port0;
	    goto loop;
	  }
	case ID_ERASER:
	  {
	    COUNTUP_INTERACTION(vm);

	    // Eps ~ (int n)
	    free_Agent(a1);
	    return;
	  }

	case ID_DUP:
	  {
	    COUNTUP_INTERACTION(vm);

	    // Dup(x,y) ~ (int n) --> x~n, y~n;
	    VALUE a1port = AGENT(a1)->port[0];
	    PUSH(vm, a1port, a2);

	    a1port = AGENT(a1)->port[1];
	    free_Agent(a1);
	    a1 = a1port;
	    goto loop;
	  }

	}