let s be a monoid and x a class of s-acts which is closed under coproducts. the object of this article is to find conditions under which all s-acts have x-precovering. we have shown that the existence of torsion-free precovering implies the existence of torsion-free covering. this work is an attempt to further facilitate the study of the conjecture that all s-acts have flat cover.

Can folding a piece of paper flat make it larger? We explore whether a shape S must be scaled to cover a flat-folded copy of itself. We consider both single folds and arbitrary folds (continuous piecewise isometries S → R2). The underlying problem is motivated by computational origami, and is related to other covering and fixturing problems, such as Lebesgue’s universal cover problem and force ...

A preliminary comparison between the Land Surface Temperature (LST) product generated by the LSA SAF and ground measurements carried out in an extensive, flat, unstressed, fully-covering rice field site showed an LST error larger than ±2K. Since then, several issues have been investigated with the aim of reducing error sources in the retrieval of LST from MSG-SEVIRI in Eastern Spain: a) a metho...

In terms of the duality property of injective preenvelopes and flat precovers, we get an equivalent characterization of left Noetherian rings. For a left and right Noetherian ring R, we prove that the flat dimension of the injective envelope of any (Gorenstein) flat left R-module is at most the flat dimension of the injective envelope of RR. Then we get that the injective envelope of RR is (Gor...

We obtain on a Kähler B-manifold (i.e., manifold with Norden metric) some corresponding results from the Kählerian and para-Kählerian context concerning Bochner curvature. prove that such is of constant totally real sectional curvatures if only it holomorphic Einstein, flat manifold. Moreover, we provide necessary sufficient conditions for gradient Ricci soliton or ?-Einstein metric to be flat....