Truncations

Let Gamma(X, ~, t, I) be an incidence geometry and let J be a subset of I. Then the J--truncation of Gamma is the geometry whose set of elements is t^(-1)(J), together with the restricted type function and incidence relation.

Let J subseteq I. The J--truncation of the coset geometry Gamma(G;(G_i)_(i in I)) is the coset geometry Gamma( G; (G_j)_(j in J)).

Truncation(D, t) : IncGeom, Set -> IncGeom

Given an incidence geometry D and t a subset of the set of types of D, return the t--truncation of D as an incidence geometry.

Truncation(C, t) : CosetGeom, Set -> CosetGeom

Given a coset geometry C and t a subset of the set of types of C, return the t--truncation of C as a coset geometry.