JUNCTIONS AND THIN SHELLS IN GENERAL-RELATIVITY USING COMPUTER ALGEBRA .1. THE DARMOIS-ISRAEL FORMALISM

We present the GRjunction computer algebra program which allows the st udy of non-null boundary surfaces and thin shells in general relativit y. Implementing the Darmois-Israel thin-shell formalism requires a car eful selection of definitions and algorithms to ensure that results ar e generated in a straightforward way. We have used the package to corr ectly reproduce a wide variety of examples from the literature. In thi s paper GRjunction is used to perform two new calculations: joining tw o Kerr solutions with differing masses and angular momenta along a thi n shell in the slow rotation limit, and the calculation of the stress- energy of a Curzon wormhole. The Curzon wormhole has the interesting p roperty that shells located at radius R < 2m have regions which satisf y the weak energy condition.