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