“…These models have been very thoroughly studied in the physics literature, in part because of connections to string theory and conformal field theory [Pol81a, Pol81b, Pol87a, Pol89, Sei90, GM93, Dav94, Dav95, AJW95, AW95, DFGZJ95, Kle95, KH96, ADJ97, Eyn01, Dup06], and to random matrix theory and geometrical models; see, e.g., the references [BIPZ78, ADF85, KKM85, Dav85, BKKM86a, BKKM86b, Kaz86, DK88a, DK90, GK89, Kos89a, Kos89b, DDSW90, MSS91, KK92, EZ92, JM92, Kor92a, Kor92b, ABC93, Dur94, ADJ94, Dau95, EK95, KH95, BDKS95, AAMT96, Dup98, Dup99a, Dup99b, Dup99c, EB99, KZJ99, Kos00, Dup00, DFGG00, DB02, Dup04, Kos07, Kos09]. More recently, a purely combinatorial approach to discretized quantum gravity has been successful [Sch98, BFSS01, FSS04, BDFG02, BS03, AS03, BDFG03a, BDFG03b, DFG05, BDFG07, Mie09, LG07, MM07, Ber07, Ber08a, Ber08b, Ber08c, BG08a, MW08, Mie08, BG08b, LG08, BG09, LM09, BB09], as well as the so-called topological expansion involving higher-genus random surfaces [CMS09,Cha09,Cha10,EO07,EO08,Eyn09].…”