In mathematics, a Weierstrass point on a nonsingular algebraic curve defined over the complex numbers is a point such that there are more functions on , with their poles restricted to only, than would be predicted by the Riemann–Roch theorem. The concept is named after Karl Weierstrass. Consider the vector spaces where is the space of meromorphic functions on whose order at is at least and with no other poles. We know three things: the dimension is at least 1, because of the constant functions on ; it is non-decreasing; and from the Riemann–Roch theorem the dimension eventually increments by exactly 1 as we move to the right. In fact if is the genus of , the dimension from the -th term is known to be for Our knowledge of the sequence is therefore What we know about the ? entries is that they can increment by at most 1 each time (this is a simple argument: has dimension as most 1 because if and have the same order of pole at , then will have a pole of lower order if the constant is chosen to cancel the leading term). There are question marks here, so the cases or need no further discussion and do not give rise to Weierstrass points. Assume therefore . There will be steps up, and steps where there is no increment. A non-Weierstrass point of occurs whenever the increments are all as far to the right as possible: i.e. the sequence looks like Any other case is a Weierstrass point. A Weierstrass gap for is a value of such that no function on has exactly a -fold pole at only. The gap sequence is for a non-Weierstrass point. For a Weierstrass point it contains at least one higher number. (The Weierstrass gap theorem or Lückensatz is the statement that there must be gaps.) For hyperelliptic curves, for example, we may have a function with a double pole at only. Its powers have poles of order and so on. Therefore, such a has the gap sequence In general if the gap sequence is the weight of the Weierstrass point is This is introduced because of a counting theorem: on a Riemann surface the sum of the weights of the Weierstrass points is For example, a hyperelliptic Weierstrass point, as above, has weight Therefore, there are (at most) of them. The ramification points of the ramified