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An infinite base has its whole powers, and surjectivity is decided through the image - #1445

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Sep 21, 2026
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Item 6's remaining analytic row — surjectivity — and a NaN on the way.

(-oo)^3 was NaN, and so were (-oo)^2 and (-oo)^(-1), while (+oo)^2 was +oo: Pow's finite-base arms did not apply to an infinite base and the polar form had nothing to say. NaN is a claim that the value does not exist, and these exist in the extended reals: -oo, +oo (by the parity of the exponent) and 0 for a negative one. The image of (-oo; +oo) under a cube is then (-oo; +oo), and RR is read as that interval where a family's image is computed (image(x^3, x in RR) is (-oo; +oo)).

Surjectivity. forall b in B : exists a in A : f(a) = b (Def 7.4.1) is the statement that B lies in the image of A under f, and the quantifier decision now puts it to the subset decision (#1432) with the image (#1442) where that image evaluates:

statement
forall b in RR : exists a in RR : a^3 = b True
forall b in RR : exists a in RR : a^2 = b False (the witness route had it)
forall b in [0; +oo) : exists a in RR : a^2 = b True
forall b in (0; +oo) : exists a in RR : e^a = b True; onto RR: False
forall b in ZZ : exists a in ZZ : 2 a = b False
forall b in {1, 4, 9} : exists a in {1, 2, 3} : a^2 = b True; with 16 in B: False

SurjectivityTest, 15 rows. BREAKING-CHANGES.md rows measured on a v2.5.0 build (NaN there). Full suite 12247 passed, 0 failed; benchmark gate PASSED.

Part of #1409.

🤖 Generated with Claude Code

https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura

Rafael-SOWNet and others added 2 commits September 21, 2026 07:41
…rough the image

(-oo)^3 was NaN -- a claim that the value does not exist -- and so were (-oo)^2 and
(-oo)^(-1), while (+oo)^2 was +oo: the finite-base arms of Pow did not apply and the polar
form had nothing to say. They are the extended reals' powers now, by parity for -oo and 0
for a negative exponent, so the image of (-oo; +oo) under a cube is (-oo; +oo), and the
reals are read as that interval where a family's image is computed.

With it, forall b in B : exists a in A : f(a) = b -- surjectivity onto B, Def 7.4.1 of the
reference of #1409 -- is decided as B lying in the image of A under f, where that image
evaluates: the cube is onto RR, the square is not and is onto [0; +oo), the exponential is
onto (0; +oo), doubling is not onto ZZ. Item 6's remaining analytic row.

#1409

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura
@Rafael-SOWNet
Rafael-SOWNet merged commit 345914f into master Sep 21, 2026
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Rafael-SOWNet deleted the odd-power-of-infinity branch September 21, 2026 08:29
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