(remove-if #'(lambda (x) (find-class x nil))
           '(arithmetic-error function simple-condition
             array generic-function simple-error
             atom hash-table simple-string
             base-char integer simple-type-error
             base-string keyword simple-vector
             bignum list simple-warning
             bit logical-pathname single-float
             bit-vector long-float standard-char
             broadcast-stream method standard-class
             built-in-class method-combination standard-generic-function
             cell-error nil standard-method
             character null standard-object
             class number storage-condition
             compiled-function package stream
             complex package-error stream-error
             concatenated-stream parse-error string
             condition pathname string-stream
             cons print-not-readable structure-class
             control-error program-error structure-object
             division-by-zero random-state style-warning
             double-float ratio symbol
             echo-stream rational synonym-stream
             end-of-file reader-error t
             error readtable two-way-stream
             extended-char real type-error
             file-error restart unbound-slot
             file-stream sequence unbound-variable
             fixnum serious-condition undefined-function
             float short-float unsigned-byte
             floating-point-inexact signed-byte vector
             floating-point-invalid-operation simple-array warning
             floating-point-overflow simple-base-string 
             floating-point-underflow simple-bit-vector))

  CCL 1.11-r16635  => (ATOM NIL EXTENDED-CHAR)
  SBCL 2.0.2       => (ATOM BASE-CHAR KEYWORD BIT LONG-FLOAT STANDARD-CHAR NIL
                            COMPILED-FUNCTION EXTENDED-CHAR SHORT-FLOAT
                            UNSIGNED-BYTE SIGNED-BYTE)
  CMUCL 19c        => (ATOM BASE-STRING
                            KEYWORD
                            BIT
                            LONG-FLOAT
                            STANDARD-CHAR
                            NIL
                            COMPILED-FUNCTION
                            EXTENDED-CHAR
                            SHORT-FLOAT
                            UNSIGNED-BYTE
                            SIGNED-BYTE
                            SIMPLE-BASE-STRING)
  CLISP 2.48       => 
(ATOM SIMPLE-STRING BASE-CHAR BASE-STRING KEYWORD SIMPLE-VECTOR BIGNUM BIT
 SINGLE-FLOAT LONG-FLOAT STANDARD-CHAR NIL COMPILED-FUNCTION DOUBLE-FLOAT
 EXTENDED-CHAR FIXNUM SHORT-FLOAT UNSIGNED-BYTE SIGNED-BYTE SIMPLE-ARRAY
 SIMPLE-BASE-STRING SIMPLE-BIT-VECTOR)
  ECL 13.5.1       => (ATOM SIMPLE-STRING
                            BASE-CHAR
                            SIMPLE-VECTOR
                            BIT
                            SINGLE-FLOAT
                            LONG-FLOAT
                            STANDARD-CHAR
                            NIL
                            COMPILED-FUNCTION
                            DOUBLE-FLOAT
                            EXTENDED-CHAR
                            SHORT-FLOAT
                            UNSIGNED-BYTE
                            SIGNED-BYTE
                            SIMPLE-ARRAY
                            SIMPLE-BASE-STRING
                            SIMPLE-BIT-VECTOR)
  ACL 11.0         => (ATOM SIMPLE-STRING BASE-CHAR BASE-STRING KEYWORD
                            SIMPLE-VECTOR BIGNUM BIT LONG-FLOAT STANDARD-CHAR
                            NIL COMPILED-FUNCTION EXTENDED-CHAR SHORT-FLOAT
                            UNSIGNED-BYTE SIGNED-BYTE SIMPLE-ARRAY
                            SIMPLE-BASE-STRING SIMPLE-BIT-VECTOR)
  ABCL 1.8.0       => (ATOM BASE-CHAR
                            KEYWORD
                            BIT
                            LONG-FLOAT
                            STANDARD-CHAR
                            NIL
                            COMPILED-FUNCTION
                            EXTENDED-CHAR
                            SHORT-FLOAT
                            UNSIGNED-BYTE
                            SIGNED-BYTE)