We present precision calculations of the processes e+ e- -> 4-fermions in which the double resonant W+ W- and ZZ intermediate states occur. Referring to these latter intermediate states as the signal processes, we show that, by using the YFS Monte Carlo event generators YFSWW3-1.14 and KoralW-1.42 in an appropriate combination, we achieve a physical precision on the WW signal process, as isolated with LEP2 MC Workshop cuts, below 0.5 per cent. We stress the full gauge invariance of our calculations and we compare our results with those of other authors where appropriate. In particular, sample Monte Carlo data are explicitly illustrated and compared with the results of the program RacoonWW of Denner et al. In this way, we cross check that the total (physical oplus technical) precision tag for the WW signal process cross section is 0.4 per cent for 200 GeV, for example. Results are also given for 500 GeV with an eye toward the LC. For the analogous ZZ case, we cross check that our YFSZZ calculation yields a total precision tag of 2 per cent, when it is compared to the results of ZZTO and GENTLE of Passarino and Bardin et al., respectively.
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