interval:delete does not work

[rongarret]

? (interval:find-all *tree* '(0 .  10))
NIL
? (interval:insert *tree* '(1 . 1))
#<1-1>
T
? (interval:insert *tree* '(1 . 2))
#<1-2>
T
? (interval:find-all *tree* '(0 .  10))
(#<1-1> #<1-2>)
? (interval:delete *tree* '(1 . 2))
#<1-2>
T
? (interval:find-all *tree* '(0 .  10))
(#<1-1> #<1-2>)