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From: Steve Bacher (C.S.Draper Lab)
Subject: Re: is quoted structure "constant"?
> Where quoted structure
> appears as second argument to MEMQ or MEMBER or as either argument to
> EQ or EQUAL et al, it is obviously not changeable hence constant.
This is not necessarily true in the case of MEMQ/MEMBER. Since MEMBER
(let's elide mention of MEMQ as it is not true CL) returns a sublist
of its second arg by definition, it cannot be guaranteed that the
second arg is unchanged. The compiler can assume constancy of the
second arg to MEMBER only when the function is being used as a
predicate (or for side-effect only, which is meaningless for MEMBER).