claim: The Maltese language is a national language.
evidence: In mathematics , the Ihara zeta-function is a zeta function associated with a finite graph .. mathematics. mathematics. zeta function. zeta function. graph. Graph ( discrete mathematics ). It closely resembles the Selberg zeta-function , and is used to relate closed paths to the spectrum of the adjacency matrix .. Selberg zeta-function. Selberg zeta function. spectrum. Spectrum of a matrix. adjacency matrix. adjacency matrix. The Ihara zeta-function was first defined by Yasutaka Ihara in the 1960s in the context of discrete subgroups of the two-by-two p-adic special linear group .. Yasutaka Ihara. Yasutaka Ihara. discrete subgroups. discrete group. p-adic. p-adic number. special linear group. special linear group. Jean-Pierre Serre suggested in his book Trees that Ihara 's original definition can be reinterpreted graph-theoretically .. graph. Graph ( discrete mathematics ). Jean-Pierre Serre. Jean-Pierre Serre. It was Toshikazu Sunada who put this suggestion into practice -LRB- 1985 -RRB- .. Toshikazu Sunada. Toshikazu Sunada. As observed by Sunada , a regular graph is a Ramanujan graph if and only if its Ihara zeta function satisfies an analogue of the Riemann hypothesis .. zeta function. zeta function. graph. Graph ( discrete mathematics ). regular graph. regular graph. Ramanujan graph. Ramanujan graph. Riemann hypothesis. Riemann hypothesis