[racket] contracts on functions that take arbitrary keyword arguments

From: Alexander D. Knauth (alexander at knauth.org)
Date: Thu Dec 26 19:45:47 EST 2013

I want to make contracts on some apply-like functions that check some  
arguments but just passes all the others (including keyword arguments)  
on to a function (provided as an argument).  If there weren't any  
keyword arguments, I could use a rest argument to do this, but that  
wouldn't work with keyword arguments.  Is there a way to do something  
like a rest argument for keyword-arguments in a contract? 

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