| http://www.w3.org/ns/prov#value | - least two units represented by formulae [II]and [III]as follows: ##STR12## wherein each of R1 and R2 is a tetravalent organic group selected from the group consisting of ##STR13## with the proviso that R1 and R2 are different from each other; (b) forming a layer of a solution of said at least two kinds of solutions over the substrate; (c) subjecting the layer of the solution to heat treatment at
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