First, check the formula for AER presented in the paper - what do you think about it?
Second, check the original Och&Ney's AER formula on page 4 of http://www.aclweb.org/anthology/P00-1056.pdf.
Align manually the following two sentences:
There was no chance it would endanger our planet, astronomers said
NASA emphasized that there was never danger of a collision
sure-links =
possible-links =
Suppose another annotator produced this alignment:
sure-links = {There-there, was-was, planet-collision}
possible-links = {no-never, our-a}
Take this as a gold-standard and your sure-links from the previous question as the set A and compute Precision, Recall and AER (according to the Och&Ney's formula).
Sum up (in 3-5 sentences) what you want to remember from reading this paper.
Formulate at least 1 question that you would like to ask the authors of the paper.
Bonus question: Check validity of the first sentence heuristic in another language - Find an article about certain event / same topic in three different non-English newspapers. Are the first two sentences paraphrases of each other?