added links to journal pages/pdf-s of:
James Becker, Daniel Gottlieb, The transfer map and fiber bundles, Topology , 14 (1975) (pdf, doi:10.1016/0040-9383(75)90029-4)
James Becker, Daniel Gottlieb, Vector fields and transfers Manuscr. Math. , 72 (1991) pp. 111–130 (pdf, doi:10.1007/BF02568269)
and added pointer to: