| http://www.w3.org/ns/prov#value | - nonwoven fabric having a strongly acidic cation exchange function is used. [0072] As described above, according to the present invention, machining for removal can efficiently be performed by using a nonwoven fabric having an anion exchange function even with a material, such as aluminum and iron, which has been difficult to be machined for removal by using a nonwoven fabric having a cation excha
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