Right, there's an awful lot of Lisp actually working...

resources/sexpr/conc.lsp

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+;; TODO

resources/sexpr/length.lsp

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+(SETQ LENGTH '(LAMBDA (L) (COND ((EQ NIL L) 0) (T (ADD1 (LENGTH (CDR L)))))))

resources/sexpr/pair.lsp

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+;; PAIR is defined on page 60 of the manual, but the definition depends on both
+;; PROG and GO, and I haven't got those working yet; so this is a pure 
+;; functional implementation.
+;; Return a list of pairs from lists `x` and `y`, required both to have the same
+;; length.
+
+(DEFUN PAIR (X Y) 
+    (COND ((AND (NULL X) (NULL Y)) NIL)
+        ((NULL X) (ERROR 'F2))
+        ((NULL Y) (ERROR 'F3))
+        (T (CONS (CONS (CAR X) (CAR Y)) (PAIR (CDR X) (CDR Y))))))

resources/sexpr/repeat.lsp

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+;; REPEAT is not present in the Lisp 1.5 manual, but it's so simple and so
+;; useful that it seems a legitimate extension.
+
+(DEFUN REPEAT (N X)
+    (COND ((EQ N 0) NIL)
+        (T (CONS X (REPEAT (SUB1 N) X)))))