premise: There are three possibilities : ( a ) **f remains <mask> to C as it is translated ; ( b ) **f moves away from C and does not intersect it at all for **f ; ( c ) **f cuts across C and there are two ordinary intersections for every t in **f .
hypothesis: the proper context for <mask> here should be a straight line or plane that touches a curve or curved surface at a point but does not intersect it at that point