{HEAD ~ The sampler} 23 wherein {TAIL ~ the wall} comprises an inner wall and an outer wall, said walls being concentric with each other 
wherein
{ HEAD ~ The sampler } 23 wherein { TAIL ~ the wall } comprises an inner wall and an outer wall , said walls being concentric with each other
HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH