in 1994 robinson (now aged 83!) published two figures in the hyperbolic plane which presents some properties of tilings of the hyperbolic plane by equilateral triangles having angles of size 2/n, where n = 7 or n = 9.

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In 1994 Robinson (now aged 83!) published Two figures in the hyperbolic plane which presents some properties of tilings of the hyperbolic plane by equilateral triangles having angles of size 2/n, where n = 7 or n = 9.