Technical Terms Graph homomorphism: A function between the vertex sets of two graphs that maps adjacent vertices to adjacent vertices, thereby preserving the graph structure.

HAMED HATAMI, SERGUEI NORINE, UNDECIDABILITY OF LINEAR INEQUALITIES IN GRAPH HOMOMORPHISM DENSITIES, Journal of the American Mathematical Society, Vol. 24, No. 2 (APRIL 2011), pp. 547-565 ...