of the Hanany-Witten effect {#shn}
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This section provides a brief review of how the Hanany-Witten brane-creation effect [@HW] is described as a smooth process. While this discussion has nothing to do with six-branes specifically, it will set the context and provide background for two of the sections that follow. The basic picture follows from general principles, but one can also find a one-parameter moduli space of exact BPS solutions describing certain versions of the process in either the worldvolume theory of a test brane in the background generated by another brane [@NOYY; @Im; @CGS] or in full supergravity [@GM], meaning that both branes are fully coupled to bulk fields and can affect each other. However, in this latter case only so-called ‘near core’ solutions are available. What happens in either the worldvolume theory [@wv] or supergravity [@3Q] is that the flux of a gauge field generated by one brane falling on the second brane generates a third kind of charge associated with the new brane.

In the supergravity description, this effect follows from the fact that the ‘brane-source’ charge of the D4-brane (see [@3Q]) is not conserved [@GM; @3Q]. This in turn is a straightforward consequence of the modified 