doc-src/Tutorial/Recdef/sep2

canonical 'cases'/'induct' rules for n-tuples (n=3..7)
(really belongs to theory Product_Type, but doesn't work there yet)

consts sep :: 'a list => 'a => 'a list
recdef sep "measure length"
  "sep (x#y#zs) = (%a. x # a # sep zs a)"
  "sep xs       = (%a. xs)"