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Hi.

We believe there [to have been an accident] at the corner a short while ago.

Is the underlined pronoun a dummy subject?

What's the function of the bracketed infinitival clause?

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Persian LearnerIs the underlined pronoun a dummy subject?

The construction is the "existential there." The actual subject is accident. Usually the existential there is in sentences like this.

There was an accident.
There is someone at the door.

http://dictionary.cambridge.org/us/grammar/british-grammar/there-is-there-s-and-there-are

Persian LearnerWhat's the function of the bracketed infinitival clause?

It is the complement of the verb believe.