ericfinster / catt.io

Revised Omega-categorical Typechecker

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Ambiguity in definition of identities

alexarice opened this issue · comments

the identity on a zero cell can be defined in two possible ways

let id = coh (x : *) : x -> x

let id2 = comp (x : *) : x -> x

@jamievicary seemed to believe that each term should either be a comp or a coh. Is it possible that the second term should not be accepted?

Right, the second term should not be accepted. The boundary of the pasting diagram (x : *) should be the empty context so that the second one is not well typed. This should be pretty easy to fix.

I could take a look tomorrow if you want

The arXiv version of the catt paper states that the boundary of (x : *) is (x : *) and not the empty context. This seems to agree with the definition of boundary on globular sums

I think we only define the boundary for k >= 0, in which case this is correct. But in the case you point out, we should actually be calculating the -1-boundary (1 less than the dimension of the pasting diagram), in which case empty is the correct answer. I just pushed a fix.