In LL, just as in COMMON LISP, there are two forms of equality: structural equality and toplevel equality.
Toplevel equality (eq and eql) tests, if the representation of two arguments is equal at the toplevel, i.e. only pointers (in the case of lists and structures) are compared. This form of equality was only provided for compatibility with COMMON LISP; its use is not recommended.
Structural equality (equal) tests, if the two arguments have the
same structure on stack and heap
,
i.e. if their external term representation is equal.