A plurality of {HEAD ~ connecting lines} are provided that couple a respective pairs of {TAIL ~ gas input} and gas output lines 
A plurality of { HEAD ~ connecting lines } are provided that couple a respective pairs of { TAIL ~ gas input } and gas output lines
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH