Anderson, Richard Feather (labyrinths); see www.gracecom.org/veriditas/.
Penrose, Roger; see http://galaxy.cau.edu/ tsmith/KW/goldenpenrose.html http: / /turing.mathcs.carleton.edu/ penroseindex. html; www.nr.infi.net/~drmatrix/progchal.htm.
Adair, David; see www.flyingsaucers.com/ adairl.htm.
Winter, Dan, Heartmath; see www.danwinter.com.
Sorrell, Charles A., Rocks and Minerals: A Guide to Field Identification, Golden Press, 1973.
Vector Flexor toy, available from Source Books (see below).
Langham, Derald, Circle Gardening: Producing Food by Genesa Principles, Devin-Adair Pub., 1978.