Ehresmann Connections for Foliations R. BlumenthalJames Hebda Indiana University Mathematics Journal 1984 text pdf 10.1512/iumj.1984.33.33032 10.1512/iumj.1984.33.33032 en Indiana Univ. Math. J. 33 (1984) 597 - 611 state-of-the-art mathematics http://iumj.org/access/