Horse collar of the Oseberg ship burial). The problem with a breastcollar harness was that the actual shafts of the cart, chariot, or other vehicle are attached to a surcingle around the barrel of the horse. The breastplate primarily kept the surcingle from slipping back, not as the primary pushing object. This results in the horse literally pulling the load, a less efficient use of the animal. The modern breastcollar has traces which transfer the pull directly from the breastcollar, but a horse collar still is more effective for pulling heavy loads. After the breastcollar harness, the next and final evolutionary stage
Matroid girth spark of a matrix. The girth of a binary matroid gives the cardinality of a minimum even set, a subcollection of a family of sets that includes an even number of copies of each set element. Determining the girth of a binary matroid is NP-hard. Additionally, determining the girth of a linear matroid given by a matrix representing the matroid is W[1]-hard when parameterized by the girth or by the rank of the matroid, but fixed-parameter tractable when parameterized by a combination of the rank and the size of the underlying field. For an arbitrary matroid, given by a independence