During the eighteenth century, the formal mathematics of Euclid's Elements were translated into geometry textbooks, and the patterns of logical deduction were codified. Under this codification, the word theorem was used to describe a conclusion that was specific to the problem at hand. In order to prove some theorems, it was often necessary to prove intermediate results that could be used in this final theorem, but would also be available for the proof of other theorems. Such a result was called a lemma.引自第287页
表示其中内容是对原文的摘抄