code: @Override
      public double compute(double a, double b) {
          if (Op.isEq(a + b, 0.0)) return 0.0;
          return (a * b) / (a + b - a * b);
      }
docs: Computes the Hamacher product of two membership function values
  
  @param a is a membership function value
  @param b is a membership function value
  @return `(a \times b) / (a+b- a \times b)`