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Do you mean a 40 hour 4 day work week or a 32 hour 4 day work week? I'm all for the latter.

Either

they're quite different though. One is just squeezing a 5 day week in to 4 days. The other is only working 4 days worth of hours.

I don't think anybody is questioning the math, I think the OP just doesn't care which. Some employers want people to be "on duty" five days a week.