Formula to trim data from original cell from other cell which contains it?

For example:

Cell A1 has:
Peter is walking his dog
Cell B1 has:
walking his dog

preferably how can I remove the "walking his dog" from cell A1

or to create cell C1 to read "Peter is"

Try:

Formula:

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Welcome to the Forum, unfortunately this is a duplicate post and as such will now be closed, you may continue in your other thread.

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