James wrote: << I suppose this is related to the Hopf fibration and/or the Reeb foliation. Yes to the Hopf fibration, no to the Reeb foliation. (There exist analogous theorems in all dimensions having a Hopf fibration: R^1 foliated by unit S^0's, R^3 / S^1's, R^7 / S^3's, R^15 / S^7's, and no other R^(2k+1) can have a positive volume foliated by S^k's.) --Dan _____________________________________________________________________ "It don't mean a thing if it ain't got that certain je ne sais quoi." --Peter Schickele