Pullback functors are strong tangent morphisms for formal schemes

Let $\operatorname{\mathfrak{X}}$ and $\operatorname{\mathfrak{Y}}$ be formal schemes over a base scheme $S$, and let $\underline{f}:\operatorname{\mathfrak{X}}\to\operatorname{\mathfrak{Y}}$ be a morphism. Pullback tangent-morphism conjecture. The pullback functor

$$\underline{f}^{\ast}:\operatorname{\mathbf{FSch}}_{/\operatorname{\mathfrak{Y}}}\to\operatorname{\mathbf{FSch}}_{/\operatorname{\mathfrak{X}}}$$

is part of a strong tangent morphism. This is one of the paper's proposed structural properties of the tangent category of formal schemes; the supplied text gives no resolution status.