In case it doesn't jump out to someone (it didn't to me), one of the authors (Shriram Krishnamurthi) is also an author of HtDP. I cottoned onto this because in

In case it doesn't jump out to someone (it didn't to me), one of the authors (Shriram Krishnamurthi) is also an author of HtDP. I cottoned onto this because in the appendix describing differences with HtDP the authors describe ideas weaving back and forth between the two books.