in {HEAD ~ step} each of the third cooktop units is preassmbled with {TAIL ~ a respective single cooking system type} prior to mounting on the base units 
in { HEAD ~ step } each of the third cooktop units is preassmbled with { TAIL ~ a respective single cooking system type } prior to mounting on the base units
OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH