I‘m doing something (tomorrow) = I hav ealready decided and arranged to do it:
A: What are you doing on Saturday evening? (not What do you do)
B: I‘m going to the theater. (not I go)
A: What time is Cathy arriving tomorrow?
B: Half past ten. I‘m meeting her at the station.
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“I‘m not working tomorrow, so we can go out somewhere.”
“John isn’t playing football next Saturday. He’s hurt his leg.”





