Proof of `Rank of a tensor killed in two quotient spaces` (1st statement)
groundedproofs/Lax342547Proofs/QuotientRank.lean · lax-342547
What this proof establishes
no assumptions
Assuming the claims on the left, the claim on the right holds — checked by the archive's pipeline. Proof code is not displayed here.
Description
Restrict the middle map to the image of the right map. Its image is in the left kernel; restriction costs at most the right-image codimension.