Hi to the genesys
Just apply the dictionary definition to a keyboard, and you have the answer to what an arranger keyboard is or should be.
Arranger
- put somebody or something in order: to put people or things in a position or order
- prepare for something: to do what is necessary to make something happen in the future
- make agreement for something to happen: to make an agreement so that something can happen or somebody can have something

Enjoy whatever you play

Bill
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English Riviera:
Live entertainment, Real Ale, Great Scenery, Great Beaches, why would anyone want to live anywhere else (I�m definitely staying put).