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10305
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(*<*)theory Overloading = Overloading1:(*>*)
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instance list :: ("term")ordrel
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by intro_classes
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text{*\noindent
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This means. Of course we should also define the meaning of @{text <<=} and
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@{text <<} on lists.
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*}
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defs (overloaded)
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prefix_def:
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"xs <<= (ys::'a::ordrel list) \<equiv> \<exists>zs. ys = xs@zs"
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strict_prefix_def:
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"xs << (ys::'a::ordrel list) \<equiv> xs <<= ys \<and> xs \<noteq> ys"
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text{*
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We could also have made the second definition non-overloaded once and for
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all: @{prop"x << y \<equiv> x <<= y \<and> x \<noteq> y"}. This would have saved us writing
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many similar definitions at different types, but it would also have fixed
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that @{text <<} is defined in terms of @{text <<=} and never the other way
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around. Below you will see why we want to avoid this asymmetry.
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*}
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(*<*)end(*>*)
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