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Published online by Cambridge University Press: 22 July 2025
Every directed graph $G$ induces a locally ordered metric space
$\mathcal{X}_{(G)}$ together with a local order
$\tilde {\mathcal{X}}_{(G)}$ that is locally dihomeomorphic to the standard pospace
$\mathbb{R}$; both are related by a morphism
${\beta }_{(G)} G:\tilde {\mathcal{X}}_{(G)}\to {\mathcal{X}}_{(G)}$ satisfying a universal property. The underlying set of
$\tilde {\mathcal{X}_{(G)}}$ admits a non-Hausdorff atlas
$\mathcal{A}_{G}$ equipped with a non-vanishing vector field
${{f}}_{G}$; the latter is associated to
$\tilde {\mathcal{X}}_{(G)}$ through the correspondence between local orders and cone fields on manifolds. The above constructions are compatible with Cartesian products, so the geometric model of a conservative program is lifted through
${{\beta }_{G_1}} \times \cdots \times {{\beta }}_{G_n}$ to a subset
$M$ of the parallelized manifold
$\mathcal{A}_{G_1} \times \cdots \times \mathcal{A}_{G_n}$. By assigning the suitable norm to each tangent space of
$\mathcal{A}_{G_1} \times \cdots \times \mathcal{A}_{G_n}$, the length of every directed smooth path
$\gamma$ on
$M$, i.e.
$\int {{|\gamma '(t)|}}_{\gamma (t)}dt$, corresponds to the execution time of the sequence of multi-instructions associated to
$\gamma$. This induces a pseudometric
${{d}}_{\mathcal{A}}$ whose restrictions to sufficiently small open sets of
$\mathcal{A}_{G_1} \times \cdots \times \mathcal{A}_{G_n}$ (we refer to the manifold topology, which is strictly finer than the pseudometric topology) are isometric to open subspaces of
${\mathbb{R}}^n$ with the
$\alpha$-norm for some
$\alpha \in [{{1}},{{\infty }}]$. The transition maps of
$\mathcal{A}_{G}$ are translations, so the representation of a tangent vector does not depend on the chart of
$\mathcal{A}_{G}$ in which it is represented; consequently, differentiable maps between open subsets of
$\mathcal{A}_{G_{1}} \times \cdots \times \mathcal{A}_{G_{n}}$ are handled as if they were maps between open subsets of
${\mathbb{R}}^n$. For every directed path
$\gamma$ on
$M$ (possibly the representation of a sequence
$\sigma$ of multi-instructions), there is a shorter directed smooth path on
$M$ that is arbitrarily close to
$\gamma$, and that can replace
$\gamma$ as a representation of
$\sigma$.