The analagous problem involving a unilateral contract is exemplified by the Brooklyn Bridge hypothetical, which Professor Farnsworth has described as "the most durable and influential hypothetical in American legal education."  Professor Farnsworth recites the hypothetical:

Suppose A says to B, "I will give you $100 if you walk across the Brooklyn Bridge." B starts to walk across the Brooklyn Bridge and has gone about one-half of the way across.  At that moment A overtakes B and says to him, "I withdraw my offer." Has B then any rights against A?  Again, let us suppose that after A has said, "I withdraw my offer," B continues to walk across the Brooklyn Bridge and completes the act of crossing.  Under these circumstances, has B any rights against A?   E. Allan Farnsworth, Contracts 185 (3rd Ed. Aspen). 

     Be sure you understand:  (1) how the R.1st Contracts First 45, quoted in the paragraph of the opinion you were reading, resolves this hypothetical; (2) how R.2d Contracts 45 resolves this hypothetical; and, (3) why the problem in the case is analagous but not identical to the hypothetical.