Ted Honderich, The Oxford Companion to Philosophy, New York, Oxford UP, 2005, ISBN 978-0-19-926479-7.
«It combines the libertarian assumption that each person possesses a natural right of self-ownership over his person with the egalitarian premise that natural resources should be shared equally. Right-wing libertarians argue that the right of self-ownership entails the right to appropriate unequal parts of the external world, such as unequal amounts of land. According to left-libertarians, however, the world's natural resources were initially unowned, or belonged equally to all, and it is illegitimate for anyone to claim exclusive private ownership of these resources to the detriment of others. Such private appropriation is legitimate only if everyone can appropriate an equal amount, or if those who appropriate more are taxed to compensate those who are thereby excluded from what was once common property.»
See also Steiner, Hillel & Vallentyne. 2000. 