@techreport{smith91-free,
	author      = {Smith, A},
	title       = {On recursive free types in {Z}},
	series      = {RSRE Memorandum},
	institution = {Royal Signals and Radar Establishment, Malvern},
	publisher   = {Ministry of Defence},
	number      = {91028},
	month       = {1},
	year        = {1991},
	file        = {Smith91-free.pdf},
}