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The spatial limits of the travel cost recreational demand model
Smith, V. Kerry, (1980)
Outdoor recreation in Montana : opportunities for excellence
Kirkpatrick, Thomas O., (1970)
Montana and its state parks
Merriam jr., Lawrence C., (1964)
Energy and environment in Scandinavia
Duffield, John, (1982)
NONMARKET VALUATION AND THE COURTS: THE CASE OF THE "EXXON VALDEZ"
DUFFIELD, JOHN, (1997)
Two Perspectives on Economy and Nature: A Review.
Duffield, John, (1998)