optimize 'last' in URAGG
diff --git a/src/algebra/aggcat.spad b/src/algebra/aggcat.spad
index 822a0178..de4666ff 100644
--- a/src/algebra/aggcat.spad
+++ b/src/algebra/aggcat.spad
@@ -1508,8 +1508,15 @@
k
last(x, n) ==
- n > (m := #x) => error "index out of range"
- copy rest(x, (m - n)::NonNegativeInteger)
+ xn := x
+ for i in 1..n repeat
+ empty? xn => error "index out of range"
+ xn := rest xn
+ -- xn is n nodes ahead of x
+ while not empty? xn repeat
+ xn := rest xn
+ x := rest x
+ copy x
find(f, x) ==
while not empty? x and not f first x repeat x := rest x
--
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