Dissecting the 2-sphere by immersions

The self intersection of an immersion i : S^2 \to R^3 dissects S^2 into pieces which are planar surfaces (unless i is an embedding). In this work we determine what collections of planar surfaces may be obtained in this way. In particular, for every n we construct an immersion i : S^2 \to R^3 with 2n triple points, for which all pieces are discs

Order one invariants of planar curves

We give a complete description of all order 1 invariants of planar curves

Immersions of Non-orientable Surfaces

Let F be a closed non-orientable surface. We classify all finite order invariants of immersions of F into R^3, with values in any Abelian group. We show they are all functions of the universal order 1 invariant that we construct as T \oplus P \oplus Q where T is a Z valued invariant reflecting the number of triple points of the immersion, and P,Q are Z/2 valued invariants characterized by the property that for any regularly homotopic immersions i,j:F\to R^3, P(i)-P(j) \in Z/2 (respectively Q(i)-Q(j) \in Z/2) is the number mod 2 of tangency points (respectively quadruple points) occurring in any generic regular homotopy between i and j. For immersion i:F\to R^3 and diffeomorphism h:F\to F such that i and i \circ h are regularly homotopic we show: P(i\circ h)-P(i) = Q(i\circ h)-Q(i) = (rank(h_* - Id) + E(\det h_**)) mod 2 where h_* is the map induced by h on H_1(F;Z/2), h_** is the map induced by h on H_1(F;Q) (Q=the rationals), and for 0 \neq q \in Q, E(q) \in Z/2 is 0 or 1 according to whether q is positive or negative, respectively

Complexity of planar and spherical curves

We show that the maximal number of singular moves required to pass between any two regularly homotopic planar or spherical curves with at most n crossings, grows quadratically with respect to n. Furthermore, this can be done with all curves along the way having at most n+2 crossings

Order One Invariants of Immersions

We classify all order one invariants of immersions of a closed orientable surface F into R^3, with values in an arbitrary Abelian group G. We show that for any F and G and any regular homotopy class A of immersions of F into R^3, the group of all order one invariants on A is isomorphic to G^\aleph_0 \oplus B \oplus B where G^\aleph_0 is the group of all functions from a set of cardinality \aleph_0 into G and B={x\in G : 2x=0}. Our work includes foundations for the study of finite order invariants of immersions of a closed orientable surface into R^3, analogous to chord diagrams and the 1-term and 4-term relations of knot theory.Comment: 6 figure

Resolution of the Surprise Exam Paradox

We present a resolution of the celebrated "Surprise Exam Paradox". We argue that if the surprise exam story is analyzed using the exact same meaning of the notion of "surprise" as is dictated by the story itself, then no paradox arises

Complementary regions for immersions of surfaces

Let F be a closed surface and i:F \to S^3 a generic immersions. Then S^3 - i(F) is a union of connected regions, which may be separated into two sets {U_j} and {V_j} by a checkerboard coloring. For k \geq 0, let a_k, b_k be the number of components U_j, V_j with \chi(U_j) = 1-k, \chi(V_j)=1-k, respectively. Two more integers attached to i are the number N of triple points of i, and \chi=\chi(F). In this work we determine what sets of data ({a_k}, {b_k}, \chi, N) may appear in this way

Framings and Projective Framings for 3-Manifolds

We give an elementary proof of the fact that any orientable 3-manifold admits a framing (i.e. is parallelizable) and any non-orientable 3-manifold admits a projective framing. The proof uses only basic facts about immersions of surfaces in 3-space

Blotto Games with Costly Winnings

We introduce a new variation of the m-player asymmetric Colonel Blotto game, where the n battles occur as sequential stages of the game, and the winner of each stage needs to spend resources for maintaining his win. The limited resources of the players are thus needed both for increasing the probability of winning and for the maintenance costs. We show that if the initial resources of the players are not too small, then the game has a unique Nash equilibrium, and the given equilibrium strategies guarantee the given expected payoff for each player

Formulae for order one invariants of immersions and embeddings of surfaces

The universal order 1 invariant f^U of immersions of a closed orientable surface into R^3, whose existence has been established in [N3], takes values in the group G_U = K \oplus Z/2 \oplus Z/2 where K is a countably generated free Abelian group. The projections of f^U to K and to the first and second Z/2 factors are denoted f^K, M, Q respectively. An explicit formula for the value of Q on any embedding has been given in [N2]. In the present work we give an explicit formula for the value of f^K on any immersion, and for the value of M on any embedding