diff --git a/libmath/desk/tests/lib/unum-edge.hoon b/libmath/desk/tests/lib/unum-edge.hoon
new file mode 100644
index 0000000..92729e7
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+++ b/libmath/desk/tests/lib/unum-edge.hoon
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+::  /tests/lib/unum-edge -- posit (%unum) transcendental edge cases.
+::
+::  Exact identities, sign, NaR propagation, domain -> NaR, and the naive-series
+::  breakdown / saturation at large arguments.  Mostly at posit32 (rps), with a
+::  posit8 (rpb) cross-width spot.  Posits round-to-nearest-even, so there is no
+::  rounding-mode variation to sweep.
+::
+/+  *test, unum
+|%
+++  u    rps:unum
+++  b    rpb:unum
+++  nar  `@`0x8000.0000
+++  s1   (sun:rps:unum 1)
+++  s4   (sun:rps:unum 4)
+++  s5   (sun:rps:unum 5)
+++  sa   (sun:rps:unum 10)
+++  sb   (sun:rps:unum 50)
+++  sc   (sun:rps:unum 100)
+++  n1   (neg:rps:unum (sun:rps:unum 1))
+::  exact identities (correctly rounded; series accurate near 0)
+++  test-exp0    (expect-eq !>(`@`0x4000.0000) !>((exp:u 0x0)))         ::  exp 0 = 1
+++  test-cos0    (expect-eq !>(`@`0x4000.0000) !>((cos:u 0x0)))         ::  cos 0 = 1
+++  test-sin0    (expect-eq !>(`@`0x0) !>((sin:u 0x0)))                 ::  sin 0 = 0
+++  test-tan0    (expect-eq !>(`@`0x0) !>((tan:u 0x0)))
+++  test-log1    (expect-eq !>(`@`0x0) !>((log:u s1)))                  ::  log 1 = 0
+++  test-sqt0    (expect-eq !>(`@`0x0) !>((sqt:u 0x0)))
+++  test-sqt1    (expect-eq !>(`@`0x4000.0000) !>((sqt:u s1)))
+++  test-sqt4    (expect-eq !>(`@`0x4800.0000) !>((sqt:u s4)))          ::  sqrt 4 = 2
+++  test-fact0   (expect-eq !>(`@`0x4000.0000) !>((factorial:u 0x0)))   ::  0! = 1
+++  test-fact5   (expect-eq !>(`@`0x6b80.0000) !>((factorial:u s5)))    ::  5! = 120
+++  test-atan0   (expect-eq !>(`@`0x0) !>((atan:u 0x0)))
+++  test-asin0   (expect-eq !>(`@`0x0) !>((asin:u 0x0)))
+++  test-acos1   (expect-eq !>(`@`0x0) !>((acos:u s1)))                 ::  acos 1 = 0
+::  sign
+++  test-exp-n1   (expect-eq !>(`@`0x33c5.ab1c) !>((exp:u n1)))         ::  1/e
+++  test-atan-n1  (expect-eq !>(`@`0xc36f.0255) !>((atan:u n1)))        ::  -pi/4 (atan is odd)
+::  NaR propagation
+++  test-exp-nar   (expect-eq !>(`@`0x8000.0000) !>((exp:u nar)))
+++  test-sin-nar   (expect-eq !>(`@`0x8000.0000) !>((sin:u nar)))
+++  test-sqt-nar   (expect-eq !>(`@`0x8000.0000) !>((sqt:u nar)))
+++  test-fact-nar  (expect-eq !>(`@`0x8000.0000) !>((factorial:u nar)))
+::  domain -> NaR
+++  test-sqt-neg  (expect-eq !>(`@`0x8000.0000) !>((sqt:u n1)))         ::  sqrt(-1) = NaR
+::  posit8 cross-width spot: identity + NaR propagation (-1 @rpb = 0xc0)
+++  test-rpb-exp0     (expect-eq !>(`@`0x40) !>((exp:b 0x0)))           ::  exp 0 = 1
+++  test-rpb-exp-nar  (expect-eq !>(`@`0x80) !>((exp:b 0x80)))
+++  test-rpb-sqt-neg  (expect-eq !>(`@`0x80) !>((sqt:b 0xc0)))          ::  sqrt(-1) = NaR
+::  KNOWN LIMITATION: the naive Taylor series diverges far from the origin.
+::  exp(10) ~ 21991 vs true 22026; exp(50)/exp(100) saturate near maxpos rather
+::  than tracking the true value; sin(10) blows up to a huge magnitude instead
+::  of staying in [-1, 1] (no range reduction).  log (atanh form) holds up
+::  better -- log(100) ~ 4.605.  Locked as regression, NOT correctness; #18's
+::  Chebyshev rewrite (range reduction) would fix these.
+++  test-exp10   (expect-eq !>(`@`0x7a57.9ded) !>((exp:u sa)))
+++  test-exp50   (expect-eq !>(`@`0x7ffe.1b02) !>((exp:u sb)))
+++  test-exp100  (expect-eq !>(`@`0x7fff.f02b) !>((exp:u sc)))
+++  test-sin10   (expect-eq !>(`@`0xc74b.a64a) !>((sin:u sa)))
+++  test-log100  (expect-eq !>(`@`0x50e9.b7f7) !>((log:u sc)))
+--