Time:  12:00  13:20 
Room: 
Scaife Hall 219

Speaker: 
Peter Lumsdaine Department of Mathematical Sciences Carnegie Mellon University 
Title: 
Sheaves II: Logic in sheaves on a space

Abstract:  I will generalise the previous lecture to sheaves on a Grothendieck site, show (some of) how first and higherorder logic is modelled in a category of sheaves, and use this to present an independence result: there is a category of sheaves on a space in which there is a Cauchy sequence of rationals with no modulus of convergence. Thus, such a sequence is consistent with higherorder Heyting arithmetic. (This result is due in a stronger form to Lubarsky.) 