# Question 8142: Bijection Guard before Constructing Both Inverse Compositions [Return to catalogue page 41](https://ocme.evemisslab.com/en/questions/page/41/) [← Question derivation index](https://ocme.evemisslab.com/en/questions/) · [Original question batch](https://ocme.evemisslab.com/en/practice/batch-20261012-advance-20261017-r02-inverse-function-foundations/#q-20261012-advance-20261017-r02-inverse-function-0017) This teaching derivation has second-context AI mathematical and bilingual semantic review, limited to the model and assumptions stated in this question. It has no human review or new Lean proof and does not promote the original question or MKO to Canonical truth. R0015-08142 · q-20261012-advance-20261017-r02-inverse-function-0017 ## Original question and givens Use the complete total map Fin(5)={0,…,4}→Fin(3) with images=[0, 0, 1, 0, 0] in source-index order. Validate every image in the declared codomain first. Equal finite cardinalities do not make the given map bijective. Give (images, bijectivity, inverse table or not-an-inverse-function, g∘f values or not-evaluated, f∘g values or not-evaluated). Do not confuse inverse functions with reciprocal function values. - G001 — Use the complete total map Fin(5)={0,…,4}→Fin(3) with images=[0, 0, 1, 0, 0] in source-index order. Validate every image in the declared codomain first. Equal finite cardinalities do not make the given map bijective. Give (images, bijectivity, inverse table or not-an-inverse-function, g∘f values or not-evaluated, f∘g values or not-evaluated). Do not confuse inverse functions with reciprocal function values. ## Definition and scope Use the original question domain, assumptions and cited MKO definitions. This item has second-context mathematical and bilingual review, with the model, answer and every arithmetic step independently recomputed from the original parameters; the source question remains a candidate. - [mko-inverse-function](https://ocme.evemisslab.com/en/mko/mko-inverse-function/) ## Step-by-step derivation S001 · impliesBefore n=5;m=3;images=[0, 0, 1, 0, 0] After complete typed total map;inverse is not reciprocal Conditions: none Validate the whole original total table first.Equal finite cardinalities do not ensure this particular table is bijective,and a zero function value does not prohibit an inverse. Step identifiers and dependenciesRule: inverse_typed_map_scope · Uses: G001 S002 · impliesBefore target=0;original images=[0, 0, 1, 0, 0] After fiber=[0, 1, 3, 4];unique=No Conditions: none Scan every original input and list all preimages of this declared target.An empty or multiple-preimage fiber cannot supply a cell of a total inverse. Step identifiers and dependenciesRule: inverse_complete_target_fiber · Uses: G001, S001 S003 · impliesBefore target=1;original images=[0, 0, 1, 0, 0] After fiber=[2];unique=Yes Conditions: none Scan every original input and list all preimages of this declared target.An empty or multiple-preimage fiber cannot supply a cell of a total inverse. Step identifiers and dependenciesRule: inverse_complete_target_fiber · Uses: G001, S002 S004 · impliesBefore target=2;original images=[0, 0, 1, 0, 0] After fiber=[];unique=No Conditions: none Scan every original input and list all preimages of this declared target.An empty or multiple-preimage fiber cannot supply a cell of a total inverse. Step identifiers and dependenciesRule: inverse_complete_target_fiber · Uses: G001, S003 S005 · impliesBefore n=5;m=3;fibers=[[0, 1, 3, 4], [2], []] After bijective=No Conditions: none For the already total map,exactly one preimage per codomain target is equivalent to bijectivity.The empty-to-empty map qualifies;checking n=m alone is insufficient. Step identifiers and dependenciesRule: inverse_bijection_gate · Uses: G001, S004 ## Reverse checks - S005 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence. - S004 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence. - S003 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence. - S002 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence. - S001 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence. ## Result ([0, 0, 1, 0, 0], No, not-an-inverse-function, not-evaluated, not-evaluated) The full substitutions and premise checks give the original answer; source identity,format and status are unchanged. ## This question review and source binding Review date: 2026-10-26 Original questions, answers, step expressions, numeric ASTs and historical records are retained. Source candidate labels remain historical and are not overwritten as formal proof. Source hashes and review receipts - input commit: 0f7be61e2c22317a4075561dc822c87d881a50db - original question SHA-256: 3892b90bed3a93c72c677c2d50be4f8960761590787ea1336fe69089924af161 - candidate record SHA-256: 293d2f13774e69705cdbf4aa8483db299767bb278792bbceed67dc8fb9675e94 - semantic review receipt SHA-256: 6ecad9d909199221a07e923f87425e80b3bdec3eed46fe5910d04fca694cae18 - question-first witness SHA-256: e8f00458977a09493b5f9f05ab9e6feec72debaf4c7d1c609d1fc95900a35a1b - Lean: NOT_RUN · human review: NOT_PERFORMED [Same-source full JSON](https://ocme.evemisslab.com/data/question-derivations/questions/q-20261012-advance-20261017-r02-inverse-function-0017.json)