To our parentsAfter the main text was ready, Sakae Fuchino kindly wrote an appendix on set-theoretic methods in the field, which also includes some of his recent independence results.

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Dissolution studies were carried out on NaCl crystals, some pure and some doped with various impurities. It was observed that etch pits associated with beaks are obtained only in NaCl crystals doped with CaC12, if the etchant reported by Hari Babu and Bansigir is used. Of the 26 poisons studied with methyl alcohol as base, only a few of the cadmium and lead salts are capable of giving beaks in NaCI:CaCh, whereas with the other poisons etch pits without beaks are obtained. These investigations reveal that the poison, the solvent and the impurity decorating the dislocation line influence the formation of beaks in NaCl crystals. The substructure of the grain boundaries in NaCl:CaC12 crystals has been revealed for the first time, by employing the etching technique. Different types of grain boundaries, junctions between the boundaries and dislocation networks have been recorded.

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