;; design points for bsl/isl/asl in 2htdp

*** '() will be the empty list 

*** bsl: current bsl - symbols + '() 
*** isl: lambda + local 
*** isl+: symbols, quoted and backquoted S-expressions 

*** structures come with dot and update forms (where?)

*** if checked signatures are added, change libraries to export signatures
    for basic things 
