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diff --git a/src/Coxeter_triangulation/include/gudhi/Functions/Function_chair_in_R3.h b/src/Coxeter_triangulation/include/gudhi/Functions/Function_chair_in_R3.h
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+++ b/src/Coxeter_triangulation/include/gudhi/Functions/Function_chair_in_R3.h
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+/*    This file is part of the Gudhi Library. The Gudhi library
+ *    (Geometric Understanding in Higher Dimensions) is a generic C++
+ *    library for computational topology.
+ *
+ *    Author(s):       Siargey Kachanovich
+ *
+ *    Copyright (C) 2019 Inria
+ *
+ *    Modification(s):
+ *      - YYYY/MM Author: Description of the modification
+ */
+
+#ifndef FUNCTIONS_FUNCTION_CHAIR_IN_R3_H_
+#define FUNCTIONS_FUNCTION_CHAIR_IN_R3_H_
+
+#include <cstdlib>
+
+#include <gudhi/Functions/Function.h>
+#include <Eigen/Dense>
+
+namespace Gudhi {
+
+namespace coxeter_triangulation {
+
+/** 
+ * \class Function_chair_in_R3 
+ * \brief A class that encodes the function, the zero-set of which is a so-called
+ * "chair" surface embedded in R^3.
+ *
+ * \ingroup coxeter_triangulation
+ */
+struct Function_chair_in_R3 : public Function {
+
+  /** 
+   * \brief Value of the function at a specified point.
+   * @param[in] p The input point. The dimension needs to coincide with the ambient dimension.
+   */
+  Eigen::VectorXd operator()(const Eigen::VectorXd& p) const {
+    double x = p(0)-off_[0], y = p(1)-off_[1], z = p(2)-off_[2];
+    Eigen::VectorXd result(cod_d());
+    result(0) = std::pow(x*x + y*y + z*z - a_*k_*k_, 2) - b_*((z-k_)*(z-k_) - 2*x*x)*((z+k_)*(z+k_) - 2*y*y);
+    return result;
+  }
+
+  /** \brief Returns the domain (ambient) dimension. */
+  std::size_t amb_d() const {return 3;}
+
+  /** \brief Returns the codomain dimension. */
+  std::size_t cod_d() const {return 1;}
+
+  /** \brief Returns a point on the surface. */
+  Eigen::VectorXd seed() const {
+    double t1 = a_-b_;
+    double discr = t1*t1 - (1.0 - b_)*(a_*a_ - b_);
+    double z0 = k_*std::sqrt((t1+std::sqrt(discr))/(1-b_));
+    Eigen::Vector3d result(off_[0], off_[1], z0+off_[2]);
+    return result;
+  }
+
+  /** 
+   * \brief Constructor of the function that defines the 'chair' surface
+   * embedded in R^3.
+   *
+   * @param[in] a A numerical parameter.
+   * @param[in] b A numerical parameter.
+   * @param[in] k A numerical parameter.
+   * @param[in] off Offset vector.
+   */
+  Function_chair_in_R3(double a = 0.8,
+		       double b = 0.4,
+		       double k = 1.0,
+		       Eigen::Vector3d off = Eigen::Vector3d::Zero()) :
+    a_(a), b_(b), k_(k), off_(off) {}
+  
+protected:
+  double a_, b_, k_;
+  Eigen::Vector3d off_;
+};
+
+} // namespace coxeter_triangulation
+
+} // namespace Gudhi
+
+#endif
+
+// (x^2 + y^2 + z^2 - a*k^2)^2 - b*((z-k)^2 - 2*x^2)*((z+k)^2 - 2*y^2)
+// sqrt(k/(1-b))*sqrt(a-b + sqrt((a-b)^2 - (1-b)*(a^2 - b)*k^2))