-mIşken [mIş + ken ]

Verb stem + mişken [mışken]

This form denotes the secondary [extra] future actions of  an already planned actions.

1. There is a planned action. ---> Bakkala gidiyorsun. [ You are going to the shop]

2.  Secondary action --->  bana da bir sigara al. [ buy me a cigarette ]

3.  Person is identified from the second part, if we don´t use personal pronoun.

Bakkala gitmişken     bana da bir sigara alıver.

Planned action          secondary action

As you are already going to the shop. Buy me a cigarette.

 [ You already planned to go the shop, while you are in shop, buy me a cigarette]

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Ankara´ya gelmişken    okul arkadaşımı da ziyaret edeceğim.

 Planned action             secondary action 

- I came to Ankara,cus it was my plan to come to Ankara]

-  While I am in Ankara, I will also visit my school friend.

- Since I am in Ankara, I will also visit my school friend.

[Since I came to Ankara]

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Mutfağa  gitmişken   bana bir bardak su getiriver.

Planned action          secondary action

While you are gonna go to the kitchen , get me a glass of water.

You are going to kitchen anyway so bring me a glass of water from the kitchen.