either make some impls private or add private-ish impls to all structures

[bshlgrs]

eg http://ds.shlegeris.com/#insertLast!,deleteLast!,deleteNodeWhichIsFirst!,getNext

ArrayList doesn't know how to deleteNodeWhichIsFirst!.

[bshlgrs]

plausibly I should just not let you have impls like that in your ADT.