[Maxima] bug in 'is' ?

[John Lapeyre]

These both cause an error (in both 5.26.0, 5.25.1, and gcl,sbcl)

 is("zebra" > 0);

 every(lambda([x],is(x>0)), [1,2,"zebra"]);

  with  sbcl:
  Maxima encountered a Lisp error:
    The value "zebra" is not of type LIST.

  gcl:
   Error in MACSYMA-TOP-LEVEL [or a callee]:
    Caught fatal error [memory may be damaged]

-- John Lapeyre