Determining programatically whether the interpreter is Guile or Clisp or Emcs

[白い熊]

Hello:

I'm developping a program which I'd like to be able to use without modification 
with Guile as the interpreter as well as Emacs lisp and clisp.

So far,  I was only programming for Emacs/Clisp, for this I used a rather crude 
check of:

  (defun kx-emacsp ()
    (not (functionp #'function-lambda-expression)))

This was enough,  as function-lambda-expression is not defined in elisp.

I would like to program for Guile as the lowest denominator.

What is the proper check I should define that would tell me whether I'm 
currently interpreting the code in Guile,  or Emacs,  or Crisp.

Thank you very much for helping me.
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白い熊