The Groupoid Model Refutes Uniqueness of Identity Proofs

We give a m,odel of in,ten,sion.al Martin-L6f type th,eory based on groupoids and fibrations of groupoids in uhich identity types m,ay con,i!nin, two distin.ct elemen.ts which are not even proposition,ally equal. This sh.ows that the princaple of uniqueness of idenhty proofs is not derivable in the syntax.