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I used to belive that I could fly

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I used to watch barny.

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I didn´t use to listen to music in inglish.

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I used to love princess.

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I didn´t used to get up late on wekends.

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I used to play in my room with my barbie's.

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The auxiliary 'did' takes the role of the 'd' of 'used to'.
did + subj + use to + verb

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In this form the 'd' of "used to" is omitted because the auxiliary 'did' does its job:
did + not + use to + verb

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"USED TO" is followed by a verb in the infinitive without "to" and this is the rule.
used to + verb
used to go
used to live

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In this form the expression "used to" is used to describe a long lasting action, a state or a habit in the past.

:) +used to+ verb+ rest

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We use used to do to talk about the past.