In the mid-twentieth century, inner-city areas designated for high-density housing tended to be, by default, reserved for rental units, according to David Hulchanski, professor of housing and community development at the University of Toronto. And there were a lot of them. Rental stocka mix of privately owned apartments and publicly funded social housingsteadily increased between 1950 and the late 1960s, when more than 100,000 units were built every year with the support of government subsidies. Social housingfeaturing rents set below the market ratefollowed a similar arc, with the federal government funding some 20,000 units every year through the 1960s and '70s. With the introduction of the condominium form of home ownership in the early 1970s, however, our cities began to change, Hulchanski says. Government funding for rentals dried up through the 1980s as austerity measures took hold, culminating in the federal government cancelling all social housing funding in 1993. Paraphrase the authors idea in 1-2 sentence