Helmers, F. L. C. H. (1979). Project planning and income distribution. M. Nijhoff Pub..
Lua i Stíl Chicago (17ú heag.)Helmers, F. L. C. H. Project Planning and Income Distribution. Boston: M. Nijhoff Pub., 1979.
Lua MLA (9ú heag.)Helmers, F. L. C. H. Project Planning and Income Distribution. M. Nijhoff Pub., 1979.
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