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You don´t say it twice always. In a clear context you may drop some parts:

((Erkek) çocuk) (merdivenden (aşağıya)) iniyor.

So there are many alternatives:

Erkek çocuk merdivenden aşağıya iniyor.

Çocuk merdivenden aşağıya iniyor.

Erkek çocuk aşağıya iniyor.

Erkek çocuk merdivenden iniyor.

Çocuk aşağıya iniyor.

Çocuk merdivenden iniyor.

Aşağıya iniyor.

Merdivenden iniyor.

İniyor.

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Earlier you said:

"Such an analysis shows that Turkish is actually making things very clear using some kind of tautology strategy (one says nearly everything twice)."

I was simply referring to what you said. I believe "not always twice" and "nearly twice" are close things.

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Yes maybe in your perfect world but I believe it´s a fact in the real world. Just google "nearly twice".

Women are nearly twice as likely as men to have depression.

China´s smartphone market is growing so fast that it is expected to be nearly twice as large as the U.S. market this year.

etc.

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