ANSI Common Lisp 3 Evaluation and Compilation 3.5 Error Checking in Function Calls 3.5.1 Argument Mismatch Detection
188.8.131.52 Destructuring Mismatch
When matching a destructuring lambda list against a form,
the pattern and the form must have compatible tree structure,
as described in Section 3.4.4 Macro Lambda Lists.
Otherwise, in a safe call,
an error of type program-error must be signaled;
and in an unsafe call the situation has undefined consequences.