See C++, Objective-C and a bunch of other languages actually in the C family.

They all share C. Real basic C.

'The Lisp family is diverse.' You interpret it in a way to make it practically meaningless.

No. The lisp family is a real thing. They all share homoiconic syntax, singly linked lists as a primary data structure, and most of them support syntactic extension through macros.

While the validity of some of my examples may have been questionable, how is Plan 9 C not in the C family? and just TRY to compile ANSI C on a P9C compiler without significant modification.

Significant modification is something different than complete rewrite.

The Lisp languages share a common core language, code, ideas, literature, community.

Derived languages like Logo, Dylan, Clojure, Racket, ... have their own core language, their own code, their own ideas, their own literature and their own community.

Yes, but they also share a history and a set of syntax and ideas... Well, except Dylan, syntax-wise. But ultimately this is an argument about terminology. And the majority of people would say that scheme is a lisp. A lisp. Not a language derived from lisp, that is independent. A LISP. in the LISP family, because that is a thing. And if you want proof that that is what most people think, you need only check Wikipedia: https://en.wikipedia.org/wiki/Category:Lisp_programming_lang...

THat's what people thought twenty years. Today this does not matter anymore.

> Yes, but they also share a history and a set of syntax and ideas...

Clojure:

    user=> (cons 1 2)
    IllegalArgumentException Don't know how to create ISeq from: java.lang.Long  clojure.lang.RT.seqFrom (RT.java:542)

    user=> (cdr '(1 . 2))
    CompilerException java.lang.RuntimeException: Unable to resolve symbol: cdr in this context, compiling:(NO_SOURCE_PATH:2:1) 

What I say...

... Well, maybe you could be right. I'm not sure. I do know that when most people say "lisp," they think of scheme, clojure, etc. as in that category.

I like to think that I can admit I may be wrong, and in this case I think I might be wrong.