| http://www.w3.org/ns/prov#value | - (a) preparing a substrate and at least two kinds of solutions, at least one of which being of a poly(amic acid) which is a precursor of a polyimide copolymer including at least two units represented by formulae [II] and [III] as follows: ##STR6## wherein each of R1 and R2 is a tetravalent organic group selected from the group consisting of ##STR7## with the proviso that R1 and R2 are different fro
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