Tabor, who was a physicist and engineer, first proposed this idea in 1950, based on his observations of the behavior of friction in a number of different systems. He observed that the force of friction acting on an object is proportional to the normal force (the force that a surface exerts on an object), but is independent of the surface area of the object. Bowden, who was a physicist, later confirmed Tabor's observations through experiments in which he measured the force of friction acting on objects of different sizes and shapes. He found that the force of friction was always proportional to the normal force, but did not depend on the surface area of the object. Here's an example of the Chinese finger trap - the only way to release the fingers is to push the ends toward the middle, which enlarges the openings and reduces the traction.  The angles that the sheets make as they approach the contact region are crucial for the geometrical amplification of friction in interleaved books. The traction forces create loads perpendicular to the paper-paper interfaces through these angles, resulting in large self-created friction forces. This can be verified by creating an interleaved-book system with $θ_n = 0$ by removing alternating sheets in two notepads. In this case, the books can be easily pulled apart, which is consistent with the theory presented. In order to better understand how to derive the differential equation for this problem it's useful to analyze the following diagram.  The first thing to note is that the problem is symmetric with respect to the central line of the book. We start by indexing each sheet of a given book by $n$ ($n=1$, middle of the book to $n = M$ at one extremity). We also define $H_n \equiv h_n/d = n/d $, where $h_n$ is the shift in position of the $n^{th}$ sheet in the contact zone with respect to its position of clamping.  As a consequence, we can build a triangle with angle $\theta_n$ and sides $1$ and $h_n/d$ such that the nth sheet satisfies $\sin \theta_n = H_n/\sqrt{1 + H^2_n}$ and $\cos \theta_n = 1/\sqrt{1 + H^2_n}$. According to Amontons-Coulomb law, this leads to a self-induced inner friction force that resists the traction when an operator pulls on an object. At the onset of sliding, the change in traction with respect to the index n can be calculated using these principles. $$ T_n − T_{n+1} = 4 \mu H_n T_n $$ where $\mu$ is the coefficient of kinetic friction, and the two factors of 2 come from the identical contributions of the two books and the two pages of one sheet. The boundary condition is given by $T_M = T^{*}$, where $T^{*}$ is the unknown traction exerted on the outer sheet, and the total traction force is defined by $ \Gamma = 2\sum_{k=1}^M T_k$. We introduce the variable $z= n/M$ and the dimensionless amplification parameter $\alpha = 2 \mu M^2/d$. In order to use a continuous description, we replace $T_n$ with $T(z)$, since M is much greater than 1. This allows us to obtain the following ordinary differential equation: $$ T'(z)+2\alpha z T(z) = 0 $$ When the boundary condition $T(1) = T^{*}$ is applied, the local traction force $T(z)$ can be found by integration: $T(z) = T^{*}e^{\alpha(1 − z^2)}$. Using this result, we can calculate the total traction force $\Gamma = 2M \int^1_0 dz T(z)$ $$ \frac{\Gamma}{2MT^{*}}=\sqrt{\frac{\pi}{4\alpha}}e^{\alpha}erf({\sqrt{\alpha}}) $$ Two intersting things about this last expresion: it tends to 1 as alpha approaches 0, meaning that it represents the geometrical amplification of friction compared to a simple linear collection of 2M independent flat sheets with local friction $T^{*}$. Secondly, it depends solely and almost exponentially on the amplification parameter alpha, which is therefore the central dimensionless parameter of this study.