Another question: https://github.com/boostorg/math/blob/develop/include/boost/math/tools/toms7... Can you elucidate which step from the original paper this quadratic step corresponds to? IIANM the whole implementation is based on the algorithm 4.2 of the paper and not 4.1, because e and fe don't figure in 4.1 and the secant step on L347 is 4.2.1 same as 4.1.1. But I don't see a separate compulsory quadratic step after 4.2.1 other than the quadratic/ipzero branch at 4.2.3, however this code seems to have such a compulsory step ie a step without the option of ipzero. L380 starts the branch at 4.2.3 and L402 starts the branch at 4.2.5, but apart from that I don't see anything in the steps given in the paper to indicate a non-branching quadratic step beforehand. Or maybe I'm missing something. Please clarify. Thanks!